More and more, I think Stan's problem isn't really all that different from Helen's. He only THINKS he knows what he wants. So he goes for it, and in the process, hurts both others and himself, then winds up with something he doesn't really value--but at that point, it's all he's got left.
I think Stan DOES want a serious relationship. But he thinks he wants a no-strings-attached one, because that's what "successful" men do (see also: Rich-hero-worship). So he does the FWB thing, then finds himself falling for the other person, but doesn't properly commit because he doesn't recognize that that's what he really wants to do. With Brandi, this meant keeping things secret until the pressure of that snapped them apart; with Lisa, it means subconsciously sabotaging the FWB line (rather than actually saying out loud, and directly, that he'd like to try something more serious). This, I suspect, will lead to a Lisa-backlash, especially because of the timing with her obsessing over Hank.
Okay, seriously, I'm claiming "Called it" rights. He'd be okay here if he didn't feel the need to reassure himself that Lisa's feelings for him (however loose they are) would survive. But he can't, so he's simultaneously clinging to her AND pushing her away to be the Babes Bling and Blow guy we're all supposed to know and love.
That speaks to an inner, underlying conflict, and I think I pinned it down in the post from the other thread.