Virgin

First off, dont have a clue if this is the right place to ask this, but ill give it a shot.

So yeah, i dont know if this is completely normal or what. But ive been going out with this girl and she wants to have sex and so do i. But whenever i feel like were getting to that point, i get so nervous and my heart start beating so fast and get somehow nauseous. She makes me comfortable and relaxed, so i dont know why i get like that. I just wanted to ask, how Can i stop this from happening. Thanks in advance for people taking time to answer. I dont know if it changes anything but Im M 24