He was desperate. All he wanted previously was to not die, to have a long life, not having to worry about anything, and be able to decide when to die. That's why the Horcruxes existed. That changed when he had a son. Now his child started school, and he had to get his life, his body back. It was complicated by those fools claiming to follow him, now he had a role to play, to not drown under those cockroaches. If they knew the real him, it would become chaos, and he'd be the first to be tortured and killed – or be rid of his body again as it stood.
He was desperate. He clung to animals and any half-sane person that came close to him, accepted his presence in their bodies. Now he had his chance, he found a teacher, he could see his son, he had hope to gain his body back, to become stronger by any means.
When he got to know of the Stone, it was evident that he had to get it. It was the easiest way. The only problem was that they took it just before he got to it. Now he had to get the Stone from the School, but he could see Him.
First he had to get stronger, and he was damned anyway, so why not use unicorn blood? It was expected from him, and it was the easiest solution, even if it was temporary.
The troll was a logical aversion tactic, since Quirrel had to handle one already to block the way to the final chamber. He almost had a heart attack when he got to know his son's role in defeating it. Well, he would have, if he had one, or if he couldn't occlude his mind so perfectly from that naïve but black-hearted youngling.
Getting to the Mirror was easy. But he wanted to use it, and Quirrel wanted to give it to him, so there was not a chance for them to get it. It was frustrating, all right, but not as much as he played it out to be. Then came his sweet, pure, adorable and brave son. And he hated how he had to act. How he had to taunt and lure him, while knowing He was only going to hate him, loath him. And his child got the Stone, so it was either them, or Him. Thank Merlin for His mother!
He ordered the fool he used so far to touch, to try killing his precious child by touch, by strangling, knowing curses may succeed, but direct contact could come out only one way.
And so he had to flee again, but his treasure was alive, He was alright, and learning. He seemed small, but full of life, so he could rest assured, concentrate on reviving himself. And he could think of any and every other thing after that…
A/N: Hoping to add all years based on the confrontations. I may change the happenings towards the end, I don't know just now. I welcome any feedback! :)