I am glad you chose to put this issue out there. Here are my thoughts.
This is a situation that calls for group therapy because you have several descriptions that can best be treated simultaneously in group. First, the difficulty in talking about your feelings is directly addressed by the process of being in a group. A good facilitator will help you cope with the anxiety and help you find your voice in group. In this instance the very process is the intervention for your condition. The find help tab at the top of the page can direct you to therapists in your area who can help you find a group. You may also want to search here.
Secondly, you’ve mentioned that others interpret your behavior as being asexual, bi, or just scared of boys. The fact that you give off this vibe will be an important dynamic to understand. Being in group is like standing in front of those multi-angle mirrors that show you how you look from different directions. Learning how you come across to other men and women will be important, because the members of the group can give you the specifics of not only what they feel around you, but why they are feeling it. It will also give you a chance to talk about your feelings about having sexual relations.
Finally, be sure to join a group with men in it so you can find out directly both how you feel, and how they feel. There is no better way to learn.