Feel it, but don't do anything about it.
i think the thing with feelings is that they can create this pressure to "do something" with them. to talk about them, to make grand gestures or start doing things to preserve a relationship so that our feelings can't get hurt or create situations that are beyond our/their comfort zone.
i think the thing I'm starting to realize is that feelings are just feelings, and that acting on them doesn't necessarily make much sense. Perhaps taking away any sense of urgency for doing anything with/about/because of them is the key to this. feel them, express and accept them to yourself, and figure out what is making you so uncomfortable about them. perhaps spend some time getting clear about what you'd like to have from your relationships that you're not getting with these new feelings in the works.
as for being involved with men who have an m.o. of keeping things casual, they might not even mean that they don't want the structure of the relationship to become more serious. perhaps they're better about compartmentalizing their emotions, or not "doing" anything with them.