Good point.
John, sexual stamina varies from person to person. Masturbation is a completely different ballgame compared to actual sex. To be honest, when I lost my virginity, I went for close to an hour. Everyone told me that I'd lose it in 30 seconds but that wasn't the case. For example, I could masturbate and be done within a couple of minutes whereas with actual sex, I can exceed an hour.
There are so many things that could cause your issue and physical attraction isn't the only thing that determines your ability to have an orgasm. I have had sex with women who were physically attractive but due to my state of mind or a non-physical attribute of the person I was engaged in sex with, there was difficulty reaching an orgasm. Believe it or not, some of the best sex I have ever had was with someone who was not as physically attractive as someone I had previously had sex with. Just because you didn't finish doesn't mean you should question your sexuality; it simply means you need to find different things that give you higher sexual gratification (positions, fetishes etc.) and experience/experiment with anything you may have an interest in.