Thank you everyone--
I really appreciate everyone's comments and suggestions on where to look.
To Black Unicorn--I say more intimate because he's described his relationship with the other women as being about no-strings fun--the women are married, and sometimes he and one of them will go on a date, be on their best behavior, and let off steam with each other.
He said when we started dating he didn't want anything serious, didn't want to get emotionally entangled with anyone. When he told me he loved me he said I'd messed up his plans.
When I was honest that I was having a hard time with the non-exclusivity, his reaction was that we should stop seeing each other because I was in pain. He doesn't want anything that isn't simple and fun, even if I'm willing to try.
Reading the comments here and in other places on the forum, I think the answer for me is to end this and not put myself through the pain. If he doesn't want the kind of relationship he and I seem pulled towards with each other -- one of intimacy and sharing problems and accepting that sometimes relationships aren't all light and fun.
Even though he wants me, he doesn't want what is between us. He's probably ignoring that right now because of the NRE. I'm not willing to be the only one who wants to try. I'm not willing to be the one who's "hard work" and "difficult" and who has to be escaped. I know it's not good to compare (though I'd argue that "just stopping" is really fucking hard)--but it's clear that I'm a lot of trouble and he has what he wants with them -- easy, fun relationships.
I'm going to end this before I get more attached.
I really appreciate everyone's honesty. Thank you.