Hi, just wanted to say, relax for a minute and read this.
No, I dont think that you are bi, or gay at all. I have had the same kind of feeling you get, don,t worry so much. If you are comfortable about your sexuality then do what you feel. Many men have felt the same way you do, just refuse that they have thought about it and keep it secret.

I think what you feel is perfectly normal and may want to just try to experiment with a man. Thats ok, as long as you are comfortable with it. There is nothing wrong with what your feeling!
Like i said, Ive feel this same way and have been with a man a few times and I felt the same way you dod. It was a fun Learing experiance for me, I was always curious.

If anything I would say your bi-curiuos at best, and thats ok. I am a straight male like you and love women. But I had to try it and it was awesome. Completly different feeling. Do what you feel you are comfortable with and maybe try it. Besides your not hurting anyone

In light of who to tell, If your relationship with your girlfriend is pretty secure, than I mey mention it to her only. It is really no one elses buisness anyway.