I too have been both sides. I got married because at that time being gay and in the military was just not done. Beforehand I played with lots of guys. Afterwards I pretended to be straight. I knew it was a lie but we were consenting adults and it was safer to be straight. It was our decision. So I was that lonely married guy who knew he was gay and could not deny or ignore the desire to be with guys. It was my choice to seek guys. It was my choice to go to to the gay side of the nude beaches. I chose to go back to playing with men. It was my choice to sleep with my boyfriend. I did not force him, nor he me. We were two men who found love, acceptance, and yes amazing sex together. My ex found a lover and moved in with her. great for her. If there's guilt, its living the lie and being with a woman. That's on me and I accept that.
I am also the guy who comes across a guy who is looking to play, to sleep together, or whatever. I do not question his motive. I do not judge when I find out he is married. That is his story. If he's a decent guy and I am attracted to him, then let's play. If it stays at the sex level, so be it. If it turns to a FWB, great. If it turns out to be more than that, awesome.
I'll get off my soapbox now.