GIRLS, PLEASE HELP ME 😭

So.. I had been in a relationship for 7 years. he didn't have a very good upbringing, and it played parts in his life as he grew older. he was very controlling, i couldn't have Facebook, changed my number several times, wasn't 'allowed' to see friends and family etc. if I was out i was every name under the sun because he thought I was with another man. anyway, one day something snapped. I left and moved back to my parents. (this was after many failed attempts at trying to make us work) I stopped contact but he called my mother crying telling her he needed to pass a message on to me as he was going to end his life. so I decided to stay in contact with him, and support him when he needed. after a few months, I met up with an old school friend and we ended up sleeping together and having a little 'thing'. now here's the issue.. my ex, (now boyfriend again) has asked me to marry him, but I can't say yes because of this guilt. my boyfriend fought so hard for us, and he's getting every single little bit of help he can, and we haven't been this happy in a very long time. I want him and this marriage more than anything. my parents keep saying it's 'okay' because we wasn't together. but the guilt is awful.

What would you do?!