Welcome to our forum.
So I take it this guy you're seeing has other (romantic) relationships, whereas you just have your (romantic) relationship with him? Sort of a secondary-relationship-type of situation.
We have a Dating & Friendships subforum
that you might find useful. And you may find many other threads (and boards) here that call to you. Post any questions that you have.
It is good that you could join us; it sounds like you have done your homework. I wish you the very best on the road ahead.