Thank you so much for all of the replies! I'm sure some of this feeling comes from my particular situation. In my marriage, I am the one who suggested that we consider non-monogamy. I wasn't interested in something casual, either sex or a minor fling with the person I had this crush on. OK, this is a bad metaphor, but I was so into him on a bunch of different levels that I was totally ready to bring this person home like a puppy (OMG, I'm so into him, he's so fucking hot, and he followed me home--can I keep him?). In the end when I asked that guy if he was into me, well, he wasn't.
In the meantime, my husband has met someone that he wants to date. I really like her, even if I don't want to date her myself, and I completely support him pursuing a relationship with her. She likes doing some things I don't (takes pressure off of me), her son is adorable, and when she comes over she just feels like she could be family. But my husband feels guilty about the whole thing since my crush didn't work out. He even offered to go get me a new puppy. The thing with my crush just sort of happened, I wasn't expecting it, and now I can't see why I would go out and purposely try to meet anyone else. I don't want a new puppy, I'm still totally miserable over the last one. Conversely, everything in my life is going great right now with the exception of that one disappointment. I don't want casual, apparently, but with that intensity of emotion there is the potential for a proportional amount of discomfort.
The person I had a crush on...I think the situation would have been like Vixtoria. I don't want any more kids, and I assume that he would at some point have wanted to do the whole get married and have kids thing. Him having a primary partner would have been fine.
I think I am just going to get on with my life for the moment, and see if I can get to the "acceptance" stage of grief.