Time
Human or spirit didn't matter much when it came to time. They both had to fight with it or against it in order to organize their lives the best way they possibly could and in the end, it still could be not enough to keep it together. As a spirit he saw it everywhere; humans that rushed through their life as fast they could to be able to try out everything, sometimes ending up in dangerous situations that could be avoided if they took some time to think before they acted. In a way he could understood their way of life. If he was limited to live only hundred years, he would be doing same thing they did even if consequences for such actions came to bite them back sooner or later. He had time to waste on nothing, to think, to step back and take it all in before trying to do anything if he wished. Humans however didn't. They were aware of their mortality and how fragile their life was so they made sure to make the best of it.
The issues with limited lifespan meant rushing forward with love life as well. During his exile he witnessed how easy it was to talk someone into being with them emotionally. Even if it stopped at harmless flirting and cheesy remarks and empty compliments, promises that could be executed within few weeks or months. Being stuck in the human world taught him a lot of things he couldn't learn on his own, things he would either ignore or not bother with at that certain time. It pushed him to find his own voice and re-discover himself. The lion spirit was used to put others well-being before his own, keep his feelings and personal opinions neutral whenever he was tackling someone else's problem created the issue of him sealing off his true self sealed away to be able to do his job. From the short conversation's he managed to snap up in the spirit world, his old self has been bitter, annoyed and distant, a personality created by one of the too many ignorant and abusive masters he himself had. That was one of the reasons he would understand Aries pain when her key was handed over to Karen, the worst master she has ever had since the beginning of time. Being exiled from The Spirit World was the lowest thing in his already empty life,the only thing he could do was to shatter and create a new alias to live under while he waited for his end to come.
His exile from his home made him realize a few things he haven't thought about before. One of them was the fact that he was –despite daily interactions with many spirits – always alone. He walked alone, he spent his short breaks alone even when he was surrounded by others. There was one empty space within him that was impossible to fill with anything no matter what he did, draining his energy and good mood. It was first when he started his random dating with as many women as possible to keep his thoughts at bay that he realized what caused that void meant.
It was loneliness.
The lack of having someone other than just a friend to talk to and share his life with.
A void created after one bad decision made when his state of mind was blinded by emotions he couldn't understand too well.
Maybe that was the decision that led to his downfall in the end.
Maybe it was just meant to be.
One reckless relationship centuries ago ended up creating this void within him that later haunted him each day, draining him into a pit of agony with pushed him into the playboy act he pulled off to fit in with others and be able to feel something even if it was for a mere second. All the dates he had been on, random flirts to forget about impending doom and pain, empty compliments to temporarily fill someone else's void…. basically anything done to forget ones mortality or other problems was not love or dedication to someone. It wasn't even friendship worth having. At best it was simple infatuation. It never lasted, it made no sense and in the end it became the cause of both pain and suffering as soon the unhealthy relationship was broken off. He was guilty acting on those feelings more than once, following them like a blind bat rather than stand against it as he should. He has lived for millennia's and yet that feeling of being connected with someone was stronger than common sense.
Another thing he learned was the simplicity of making promises to be with someone forever. While the lion spirit never promised them right out to stay by their side forever flat out – even if his words were always one step away from doing just that- there was a difference between "the rest of my life" and "until the universe stops existing". For him, eternity meant forever. His promise of eternity would not end until he was either somehow killed or The Spirit World stop existing. For a human, it ended either after the relationship crashed or one of those two died. There was no forever for them, just a temporary time of being with someone until their life gave up on them and their limit was reached one or other way. In a way he admired human race and their dedication to live their life to full no matter what happened. The limits set out by nature and the lack of enough time to do it all made them to push themselves as far as they could. No matter how small chances they had to succeed, they made it work. Maybe that was what made their love last. Maybe that was what kept their feelings intact once they found their beloved one. The limit of how long they could be with each other made their love to never die. Their entire being was held in a glass without any breathing holes, slowly killing their body and mind until they became one with earth but their emotions were always intact no matter what happened.
Could he promise Aries an eternity and live up to it?
Would his love for her never fade, or become stained and disappear with time?
Would they face the same situation as they did back then or would their doubts they had disappear?
After being friends for long time, their feelings changed. When and why that change happened was hard to pinpoint today, only thing he knew was that one day they both ended up falling into a pit of emotions none of them were ready for. They acted upon them not knowing what to expect, trying to keep together but pulled of an act as if they were not as close as they were. There was more to think about than just their personal feelings for each other. None of them wanted to create a situation where their partner had to either pick a side or give up their current living situation. They had no idea what rules they had or what they were trying to accomplish. And most of all, they didn't understand each other as well once they became a pair. It took long time for Leo to discover why their relationship back then has ended in a painful commitment and ended up with an agonizing split-up. It was first when he felt his life fade away nearby Karens grave that he understood why they fell apart before anything had begun.
None of them had taken time to find what they wanted out of such commitment.
None of them had considered the other ones feelings about it, and they couldn't tell each other what they wanted because they themselves had no idea what they thought about that kind of commitment.
None of them had invested any time to understand that concept before they became a thing. Like two magnets they spiraled slowly closer and closer until they ended up in the same place.
It was painful to think about it. Even today his soul felt tormented as soon a faint memory came back to taunt himfor his failure to keep someone happy. Someone who got closer to him than anyone else. A comrade that could read him like open book no matter what kind of act he was playing. Thanks to his experience as Loke, a mage of Fairy Tail, he finally found out what such commitment would require. His act as a playboy may have been one of a huge mistake, on another hand it forced him to reflect on his ever growing void inside him. Today he knew who he wanted to be to that someone he one day hoped to once again have by his side. There was no doubt in his mind that he was able to live up to his promise of eternal commitment to someone. He was not someone who broke such promises no matter what happened.
Once again, time was not on his side in this matter.
Thousands of years separated him and Aries apart. He was much older and experienced spirit who had more time to listen, observe and learn and even if he failed on the reflection part, he still processed more knowledge about this than her. There was a time when the spirit of ram wasn't even considered as a constellation. There was a time when she was so broken that even his support failed to help her through her dark times. Not even the light of Regulus could erase the darkness and pain caused by being labelled as nothing important. He was the only spirit that refused to give up and kept her company during that time, trying to keep her hope up of being discovered by humans and be given a name.
This was why he haven't told Aries the truth. Why he was still silent about the fact that he still loved her more than before. Why he refused to give in despite his screaming soul after someone to connect with. This was why he kept his neutral act whenever he was with her, their friendship staying as strong as ever. If this was the only thing they could ever be he could accept it. Their friendship had no boundaries or limits. They trusted each other with their lives because in the end, they both had been broken and shattered in different ways, both of them picking each other's pieces to rebuild what has been lost. Leo was giving her needed space to learn on her own. If she ever decided to choose different path or stay as she was now he would live with it no matter how hard it would be for him to stay away.
They both had time to do whichever they decided was best for them. In the end it didn't matter, his love for the timid spirit of ram would never fade.
His love for her would give him strength until the end of time.