21 yr old Virgin finding it difficult to gain erection

I am 21 years old and as of yet have not had sex. Had multiple opportunities, but could never gain an erection when the time needed it. Even as things were getting hot and heavy and I was with someone I found extremely attractive my penis was just not reacting. I fear that this might speak to something larger as I believe I have not been sexually aroused in a long time. I won't get into my own self-diagnoses because I would like to hear if anybody has a clue of whats going on. I will say that it could be the result of Catholicism, sexual repression, low self-worth, low self-confidence, and my long time acceptance of never getting laid.

Edit: I don't watch porn very often nor do I masterbate excessively, maybe once or twice a week.