It's not one person's fault, but here are a few observations:
- If someone tells you repeatedly that he's not your boyfriend, he probably doesn't want to be.
- If you find yourself constantly defending yourself because "[you're] not her boy friend" then you might want to reevaluate the situation.
- Casual sex between friends is fine. If that's all it is. And that's rarely all that it is. That "fuck buddy" dynamic is usually one-sided; one of you is usually lying about how you feel and becoming emotionally attached.
- If the above situation occurs with your fuck buddy, you should stop having sex. Yes, no matter how horny you get, find someone else. Or use your hand.
I don't say those things solely from observation. I've been in that situation. I've been the one who believed the relationship was nothing more than sex and I've been the one who became emotionally attached. I've been the one who thinks "if I just hold on, she'll see that what she was looking for is right in front of her!" (blech- a little hollywood puke). I've also been the detached one who's allowing the other to fall for me.
It has never ended smoothly and someone's heart has always been broken. At least that's my conclusion from my highly anecdotal evidence.