Do men somehow lose interest in female friends who are in relationships (even if the friendship was always platonic)? Why?

I've had a few friendships with guys develop in the last few months and I can't help but notice that these friendships faded some time after I mentioned having a boyfriend.
Now, these friendships were always platonic from the start (at least to me). And I never noticed anything sexual/romantic hints from these men either. Yet, somehow, it feels like they lost interest in this friendship when they realised I'm not single. I do have a few other close male friends and everything seems fine with them, so I'm assuming I'm not driving them away. And this was not something I experienced back when I was single. In general, it just feels like men are uncomfortable around me once they find out that I have a boyfriend.
Do men somehow feel like they're crossing someone else's territory, or worried about your female friend's jealous boyfriend? I just can't seem to wrap my head around it and it's made it difficult for me to maintain friendships with men.


Source.