Help! Seeing two guys in different ways... have to make a choice?

I have two friends and all three of us work together. I started having a physical relationship with one guy who I am very attractive to and he is very attracted to me but says he can't be in a proper relationship because he can't give the time commitment and says he may be moving in the future and I am settled in my career here and am going for post graduate degrees in town. He says that I deserve way better than him. He is even encouraging me to find a guy who can better meet my needs and says we can still see each other casually in the time being but we will remain friends forever. He knows that I have been hanging out with another mutual friend but nothing physical ever happens but he is more stable and has more to offer and we have so much in common and can talk all night like we were in high school again! Last night he started kissing me and I ended up sleeping with him. I don't know where I stand with him, what it meant, or anything at this point. The other guy wants to have a rendezvous with me tomorrow but I can't sleep with two guys at the same time! I don't know if I can actually tell him what happened; I am not at all promiscuous so this very out of my element. Should I continue with both guys or should I tell the first guy what happened between me and the second guy? At this point there is no expectations with either guy and I am not necessarily looking for a serious relationship but I am starting to think it might be somewhat nice being committed with another person which I haven't been since my divorce.