I don't think sex is the problem here. You'll know whether you enjoy it and with practice will get to know what you like. That part gets more comfortable with time. I was 25 the first time I had sex.
Your fear seems like it amounts to panic at being left. Really you can never be abandoned because you have everything you need within yourself. From the looks of it you have walls erected all around in an attempt to preempt anyone getting close enough to hurt you when they leave. I agree with Angela that this probably comes from a time so long ago you might not even consciously remember it! Dig down to the root of your fear of abandonment and let that go and I think the sex issue will hardly phase you. When you realize the massive amount of strength you have inside, everything becomes a pleasure or a challenge -- never a terror.