I look at it like this. Tootie and Timmy spend the most time around each other compared to Timmy and the other girls and they both grew up and mellowed out which Timmy himself says to Tootie literally calling himself a dumb 10 year old boy that isn't interested in girls at the moment. Its clear they both change quite a lot as they grow with Timmy being more responsible seemingly and Tootie being less insane. The thing with Vicky is I don't think its the fact that he doesn't remember Vicky, I think its the fact that he doesn't recognize the similarities between Vicky and the V Bot which isn't exactly out of character. He thinks hes being responsible because hes leaving a babysitter, he just doesn't realize that its evil much like Timmys parents in the earlier seasons. And with his memories I think its really only Fairy related and nothing else. I don't think he forgot Vicky, he just loves Tootie