Is it normal to want to have sex with a certain person so badly?

I'm asking this question because I want to have sex with one of my friends. I've never felt this way about him we've always been just really good friends but about 3 weeks ago I've just been having the urge to fuck his brains out.He has a girlfriend I don't want to break them up or anything I don't even want a relationship I just want to have sex with him.Is It Normal