Re: What is he thinking?
I'm sorry but this guy is not your "friend" in that by kissing, and suggesting a "friends with benefits" relationship with you, he is putting you in the position of cheating on your current LTR. WTH?
Something just does not seem right. It would be one thing if he said "I want to be with you, I'd break off my current relationship if you break off yours so we can see if this works?" But instead he suggests friend's with benefits? He doesn't even sound jealous of your LTR and doesn't seem worried about you cheating and compromising your values. So, no, that does not sound like love to me, not even like the kind of friendship where someone cares about your best interests over their own sex drive.
Is your reason for not being with him ONLY because you are both in LTRs? Or do you love your BF?
If you love your current guy, stop dating your friend! If you are not serious, well, that's the difference between a LTR and a marriage. You have no obligation to stay in a LTR.
But you are playing a vary dangerous game spending time alone with this "friend" when you're in other relationships. One of the things that makes people fall in love is being together while doing things they enjoy. You're spending time alone with a red blooded man doing fun things. I'm surprised it's taken him 6 years to cross the line. I'm also surprised both your significant other's aren't concerned about your friendship.