But, we recently slept together (it felt right and was great).But, we are technically not exclusive (meaning, we talked prior to sleeping together and said that we were both able to date others, if we wanted).
I don't know about "cheating", I don't think that everyone's idea of what may or may constitute "cheating" is really relevant here. If "yes" then as her partner, why is he choosing that behaviour?
Concealing it from her doesn't make it okay any more than a man having an affair is okay so long as his wife doesn't know. Why hasn't he spoken with her about it what is your role in all this and how come you know so many details of their relationship?
If he really likes her...he'll wait for her for as long as he needs to...anything less probably not..it cheating..if they're just "dating" and not in an "exclusive" relationship..sometimes things can get muddled until someone actually brings up the topic and establishes where they truly are in the relationship.
I am very happy (and he said that he is happy when he is with me) and like him the more I get to know him.
These two people appear t have a communication problem and possibly a compatibility problem -- but that last can't be ascertained if they don't communicate.