My boyfriend once dismissed my experience with being sexually harassed and it’s the most he’s ever hurt me

While it's good to be weary in this world, if he still has issues from his exes he should talk them out, from a trusted confidant to you to a therapist, which ever one he feels comfortable talking to. He isn't with his ex, he is with you and shouldn't bring past relationship issues into his next one so willingly. It's not an easy cycle to break but he did do this completely wrong. It really was emotionally damaging to side with his coworker over you. This is a major milestone in your relationship because you found out a few things: he wasn't fully over what his exes did to him, he wasn't emotionally ready to be there for you, and he let you down for siding with the wrong person in this situation.

/r/TwoXChromosomes Thread