<human>: Give me the gist of the text in a nutshell

My boyfriend "Bob" used to date "Melissa". They had to part ways to different states after graduation -- Melissa wanted to keep dating, Bob wasn't sure. They kept in contact throughout the summer until he definitively broke things off. He met me a couple weeks later and we've been dating for 1.5 years now. Maybe I'm overly sensitive about the situation because he once told me they "definitely would've continued to date" had distance not become an issue - this was hurtful to hear, but hey, we had only been dating a month at the time. Word vomit happens.

Melissa reaches out periodically, and Bob responds (as he should, in respect to their past). Contact has petered out naturally over the last 1.5 years, and their last contact was 6 months ago. Bob, 2 weeks ago, decided to message Melissa via facebook on my old backup laptop and left it open. Yesterday, I opened said laptop and there was the message. I'm upset and here's why:

I think it's disrespectful of me for him to *initiate* contact with an ex without at least casually mentioning it to me. Particularly since it seems out of the blue, 6 months after no contact with her. Had he mentioned it to me, I'd have felt fine with it! Instead, it feels like something's been done 'behind my back' or something like that. He says he felt the need to reach out because he feels bad since he was the one who broke up with her / wants to check in on how she's doing. (??) I think that's a little condescending to her, but that's a separate issue. 

He does respect my position, and won't do it again. He doesn't necessarily agree that he did anything wrong, though, which is why I'm asking here what you all think about the situation. We will both be reading the comments.
<bot>: I think it's not appropriate to initiate contact, out of the blue, with an ex without mentioning it to your current partner. He doesn't see any problem. Maybe I'm being oversensitive but what do you all think?