Useful info:
OK so I'm an 18 year old male.
I am sexually active and have had 3 sexual partners.
Two of which were long term relationships and one was a drunken mistake.

I find women attractive and want to have sex with them like any normal person, but when it comes down to sex I'm just like "Meh"... And don't want to have sex suddenly ...
I don't understand why I am like this but I have been like it ever since I can remember.
I am only not like it when I love the person...

Is this normal ?
All people I know can jump into bed with a woman, have sex without feeling as I do.

(I have been told by many) I am very attractive and I can attract some really beautiful girls.. Somewhere down the line I have the chance to have sex with them but then my sex drive vanishes and I'm there like "Meh".

It frustrates me as I lead these women into bed then just totally reject them... wtf is wrong with me :S

Any help is appreciated, thank you

(P.S) These women arn't 'Easy' so I doubt it's I want someone hard to get :/
I have had sex (Just to clarify)