>>1 You feel guilty about making a guy horny? He's gonna feel that way with or without you, love.
Do not- and I repeat- DO NOT think of yourself as needing to "fix him".
No. Just no. Wrong mindset entirely. Saying it's your fault or that you feel guilty or that you need to fix him, is all just wrong. You just need to talk to him.
A lot of relationship problems brought up on here are solved with rule number one of salvaging a relationship: communication.
Bring up that you believe he's changed and that you're not comfortable doing pervy stuff (and you shouldn't, you're 15).
You really shouldn't have given him a blowjob either, because as I'm about to point out, whether it's consensual or not any sexual activities with him is considered statutory rape (if you're living in the US). But personally, I don't feel like any 15 year old should be giving out blow jobs.
Anyway, you're not currently dating him, right? Then you don't have to bring this up. There is no "fixing". He's his own person and all you can do is pray about it if you're religious.
What pisses me off is if he's trying to make you feel responsible for it over some bullshit like "he remembered "stuff"". His mind being in the gutter isn't your fault. You should also let him know that isn't his fault. Like I said, he's a teenage boy, as soon as they're sexually active they generally want to do it 5-6 times a week. This is normal. He needs to know that.
If you really wanted to, you could bring up how this change is making you feel uncomfortable, because you miss the nice guy from last year. Then encourage him, he needs you to know, as much as movies, shows, and news media would like you to believe, sex after marriage is not an impossible request. My cousin and her boyfriend have been dating for about five years, going to get married this fall, and they've never had sex.
After that, tell him to look up ways of abstaining from sex if he truly wants to wait till after marriage. Hell, maybe he just needs to jerk off more?