Ted never told her the whole story, but Tracy always had a feeling there was more to his relationship with Robin than he'd ever let on to her. She saw how Robin still looked at him sometimes, and she realized that some wounds never truly heal. Sometimes, no matter if you let go of a person or not, there will still be a part of you that loves them. Hell, there was always going to be a part of her that loved Max. He wasn't her first boyfriend, but he was the first man she'd truly loved. But it didn't make her love Ted any less.
That's why she never made a fuss of the situation. Life works in mysterious ways, and her journey to Ted had taught her that. Besides, she trusted the both of them. They'd never do anything that would hurt her. If she dwelled on it, the only thing to come of it would be heartache. She'd end up thinking of all of her own losses, and then she'd want to break out her ukulele and sing "La Vie En Rose," and it wouldn't be pretty. It was better to focus on the here and now.
Their relationship was still relatively new, but despite that she realized Ted was something special. He was the one, and she thought she'd never find another one. She'd always thought people only got one shot, and look where that had gotten her. Eight years of loneliness, and she'd broken a really great guy's heart by leading him on. Because the truth was, that's exactly what she'd done. She knew she didn't love Louis, but she'd been with him for over a year. She just hoped there wouldn't be a novel written about her someday, like Ted had been written into The Wedding Bride.
She was learning that sometimes you had to just make the best of whatever time you got with someone. She was finally ready to let herself be happy. Life wasn't always gonna be easy- it was certainly a long and difficult road at times- but the journey was always gonna be worth it. And she thanked every god there is or ever was or will be and the whole universe, and anyone else that she could possibly thank, that she had found Ted. Because for whatever it was worth, everything in life was a lesson. And she couldn't forget that.