Pretty much this for me too. It's a feeling of longing, need, desire. My breathing gets shallower, pausing briefly while entranced by whatever sweet being captured my attention. I think, that's all I want, why is that so elusive? Then his gf/fiance/wife appears, but oh it was a nice moment while it lasted. :icon_wink
I start to maladaptive daydream about the person (always, always, ALWAYS, a male) and paying attention to every detail about them. Even shit I don't like about them, I don't give a fuck. I see us going on dates, just bullshitting, cuddling doing whatever. It's really sad, like, "Oh my god that's my man." "I love him anyways," "He's mine." etc. But I've never had a boyfriend, so. I don't know. Ugh.