I can't have an orgasm

I need some help. I am having problems in the bedroom, which I'm sure is not an uncommon problem you're faced with. But for me, it is about the worst thing that is going on in my life. I recently started a relationship with a girl I've known, and when we have sex I can't have an orgasm. Everything she does FEELS good, and I'm definitely attracted to her. But when it comes down to having an orgasm I just can't. I'm not sure if its a psychological thing or what, because in my last realtionship I had orgasms all the time and the sex we had was nothing in comparison. In my current relationship i have explored my sexual side a lot more, and we interact with eachother more. ie more foreplay, my stamina has increased immensely. Right now I'm very confused and would GREATLY appreciate any feedback you have to offer. A good friend of mine suggests that it might be because there is a lack of emotions, since this girl I'm with is more of just a sexual partner and we have no emotional ties, at least I don't for her. I really need the help though, because I'm starting to feel like a freak. Any tips of how I can turn my mind off during sex, and stop focusing on having one, would be great. Because she's starting to catch on that I fake my orgasms, and I honestly don't believe it's anything that shes doing.