Summary in bullet points.

• After two years of dating, they get engaged. Pretty normal. BUT NOW IT HAS BEEN AN 8 YEAR LONG ENGAGEMENT.
• OP starts a sport that is likely quite good for her natural build: weightlifting. Builds muscle mass. Partner complains out of jealousy and disliking her body transformation. Guess what heavy muscle turns into when you stop lifting? Fat. It turns to fat. And, yeah, the body has a difficult time resetting lower. Convenient for him that you currently believe:
• Rejects kissing because a peck on the cheek is more intimate? Yeah, no. It's not.
• Rejects physical contact in a demeaning manner by wiping away the spot where you touch him like you have cooties.
• Mother whittled away OP's self-esteem through constant criticism. Great for him! You've been so primed for direct abuse and low self-esteem that all he has to do is something moderately less direct, and you won't actually catch that he has done the exact thing your mom did your whole life: made you feel like shit.
  

I just feel STUPID and know that all of these issues between us are my fault cause I’m the one who got fat and I’m the one who is unfuckable.

Only, when you were doing stuff to keep your body healthy you were "unfuckable" too. Can you see this is an unwinnable situation for you, but a pretty good situation for a guy who wants the convenience of a what appears to be a relationship to the outside world without having to actually do the work to physically or emotionally be in one? Your self-esteem is so beat up, you don't even realize that you have a beautiful body and that many men would celebrate you at your current weight and would have celebrated you during your weight lifting phase. It's true that we are attracted to what we are attracted to, but that doesn't mean that one person's likes and dislikes are the entire world's likes and dislikes. Life is way too short to be living the way you have.

You could drop 90kg right now--no diet or exercise needed-- if you are ready to. If you aren't already, get into therapy and take the steps you need to prepare you for the next phase of your life. Mourn the 10 years wasted, and just know that 30 is young.