Noticing girls after they've gotten into a relationship

Well, I would assume it's because you never considered them as a possibility and when someone else does it sparks your attention. I would also bring to note the idea that you are attracted the to way they act around their boyfriend. Meaning that you want that kind of relationship with someone, and when you see it expressed you are therefore attracted to them. Also, this has happened to me SEVERAL times as well, you are not alone in this respect.

Jam it back in, in the dark.

Originally Posted by Rychord

My advice to you is to really not waste too much time considering what might have been

I agree, don't worry about going after something that has already past. I would also that that I don't suggest 'looking' for a relationship. I find that always gets you somewhere that is shallow or unpleasant. Find someone you get along with first, then consider the idea of a relationship.

There's nowhere I can't reach.