Will I ever trust him again?

Question

My boyfriend and his ex dated for three years, freshman to senior year, and me and him met the middle of our senior year. it was a bad relationship, and he wanted out of it and they broke up a month after we started talking. She took a very very long time to stop messaging him and calling after they broke up, which I had to be “okay” with because I didn’t want to be too pushy, since he had an issue with her being so controlling. Fast forward a little over two years, and we’re living together. He goes on a guys trip one weekend and comes back, everything seems fine, our two year anniversary passes and we’re happy. I find out a couple days after that on his guys trip, his ex had messaged him to see how he was. She was flirting at some points and saying how she “definitely misses all of him,” and he said he was high so he was just saying “mhm sure” to those things. He deleted all of that before I found the Instagram DM where he was apologizing for stalking her Instagram and liking a picture, in which he decided to make a comment about her big butt. It’s been several months since then and I’m struggling so bad. I love him so much and he’s trying to hard, he really is. I know he’s sorry and I know he regrets it, I just cannot understand why he would do that to us??? We were happy, and now all I think about is if he’ll do it again. Please offer insight, or let me know if your relationship worked out after he cheated.

Answer

Eh I mean this was bound to happen especially since he broke up with her a month AFTER yall started talking!!! Like wtf... why talk to a guy who is in a relationship????

Answer

He cheated on her with you. So why do you expect him not to cheat again?

Answer

Did you know that he was in a relationship when you started talking to him ? 
Looks like he jumped into another relationship with you without ending or have sometime for himself after braking up with her , he never really felt the braking up  
Hope things work out for you two , talk to him ,tell him to block her number , but then again he can always unblock her ... it has to be him wanting to block her .

Answer

What they do with you they will do to you is a true saying and almost all of the time it's true. 
He really didn't have time to work on himself he jumped into a relationship with you, I would say that they probably always talk they may even get back together you never know. Just keep your guard up.