Dear Unsure and Unloved
To borrow a phrase from Bridget Jones, the amount of fuckwittage going on here is incredible.
This guy has cheated on you twice (that you know of), tried to involve you in sexual shennanigans and drug use that you are not comfortable with and to top it all off he has the nerve to defend his cheating. This makes it obvious that he has no intention of changing his ways or compromising his behaviour.
Relationships are based on trust and mutual respect, neither of which he is showing to you.
You deserve much, much better than this. It's hard to say goodbye when you've been together for so long, but this relationship has run its course and from what you say you do know that. You're off to different colleges and this is a great time to make a clean break. Let him go and be an idiot somewhere else while you go and have fun and meet new (decent) guys.
Get out of this toxic relationship before it damages your self esteem any further. It may hurt in the short term but in the long run you'll be so, so glad you've finished with him.
Readers, do you agree with Assumpta? What advice would you give in this situation?