Hi @luftwink , change a few details and I could be your husband.
I was in a long distance relationship at 24. We met backpacking, lived in different countries, so visited each other a couple of times, but most of the time were apart. Just as I was coming to the realisation that this relationship wasn't going to work, I met my DP on a night out, and very nearly did something stupid.
So I broke up with my long distance relationship over Skype, and then pursued DP.
Fast forward 11 months, and me and DP are having a (very) surprise baby. A couple of weeks later, when the dust has settled a bit, I realise that when ex finds out about this she's likely to be really fucking hurt.
So I send her an email. I wanted to explain what had happened, reassure her that there hadn't been an overlap, and that my reasons for splitting up were due to the long distance, not because I'd met someone else. I went a bit overboard, and said "I really did love you and part of me always will"
It did not go well. Ex's only reply was "That really fucking hurt". And then DP found the email. She was also "really fucking hurt". We came within a knats wing of splitting up, and 17 years later DP still flinches if she hears ex's name.
Here's the thing though, I don't think it was wrong to say what I did. I do think it's possible to love more than one person at once. We don't tend to, because most relationships end acrimoniously, and then you move on. But when there's noone at fault, it's not quite as cut and dry. Just because I ended things with ex, and met someone new, it doesn't mean that I stopped feeling anything for ex. The fact that those feelings still existed, and that I didn't want to upset ex didn't mean I was any less committed to DP.
Obviously, X number of years on, I'm not still in love with ex. I recently heard she was married, and was really happy for her.
Obviously your situation is slightly different, your DP messaged something obviously sexual, and it sounds like there was a bit of overlap between his relationships. But what you're worrying about is probably the same as my DP "Would he still be with her if not for the distance"
The answer is "Maybe". But does that really matter? There are no such thing as soulmates. There's only right person, right place, right time. The ex missed out on one of those three, you didn't.