Have you ever found yourself newly involved with a man, only to find out later on that he was already in a long-term relationship with someone else?
Yes. A guy who told me he was single. More than a year later he told me he'd had a secret gay lover all along who predated me, for whom he was leaving me.
Except the other guy fucked him over, and then my "ex" came back to me for advice & support. Well, fine, I help almost anyone who asks me, even if the've broken my own heart. I'm tougher than tough, and was raised to put others ahead of myself.
So I helped him, still do to this day. I'll never invest my love in him again, however, which is his loss, in my selfish opinion. Plus I have a partner now, with whom I'm totally loyal, totally monogamous, totally in love.
This other guy had his chance, and he blew it. Now he remains single, still fucked up and approaching 60 years old. You make your own bed, and you lie in it.