In my personal experience, yeah I definitely act different with each person. And how much I trust them affects what I'm willing to try with them.

As for how often I think about them: I barely think about my one night stands(probably forgotten most) except for maybe 2 that were really good, but I still only recall it maybe once a year at most. As for FWBs, I still occassionally(maybe every couple of months) think about one that was so bad, I don't even know why I had sex with him more than once. I realize I think about this more than the good ones because of how much I regret it. Other than those, I think about sex with my current boyfriend 24/7.