Is it normal that i desire guys most when they have a girlfriend?

Normal I guess, but not good.

Normal.

I can be single & never have a girl notice me but as soon as I'm in a relationship, even if I'm never seen with my girlfriend so not known to be taken, I feel like other girls are a lot more interested.

I think part of it is that I am no longer showing interest in them so I give off a super confident vibe as I have no need to impress. They get that feeling that they can't get you which makes them want you more.

I think guys (in a happy relationship) give off a happy, confident vibe that girls find really attractive.
I once thought this guy was adorable and was very attracted to him because he was so sweet and happy with his girlfriend, and before seeing that I had no interest.

I'm not like that. I don't want what isn't mine.

You all do.

Three words: instant peer approval.

This is so normal that we guys have a saying about it.
When we are out at a club, and have a gf, we could go home with any one of several girls, but when we don't, we always go home alone.
Life sucks sometimes.

It's normal. I read up a long time ago that women tend to have more of an attraction to a guy if he has a partner than they would if he didn't.