Embarrassing issue?

I started dating this girl. The sexual tension was sooo high and then... The last two times I've tried to sleep with her it's like my libido is shot. This has never been an issue before, but now it's like I have this added pressure and I just can't get turned on.

I feel terrible and very embarrassed. I feel like this has divided us a bit. I tried talking to her last night about it but she just says quiet. I feel like I made her feel unattractive or something and it sucks because I find her soooo attractive! I feel like now I might get hurt because she may bail on me because of this, so I'm almost thinking of backing away.

I'm only 30 years old, I'm in good health... I just don't understand it. I really don't want this to ruin my relationship. What should I do?