Cant Stop Thinking About It

I cant stop thinking about what it would feel like to be fucked by another man. I want to be face down and ass up with a nice big cock pounding my ass. I have been curious a long time but cant get past being nervous and just doing it. I go on websites and jerk off with men and put things in my ass while jerking off with them and it feels great. Does anyone have any advise on how to get over being scared and nervous and going through with it for the first time?