I don't think you are incapable of devoting intimacy towards another person, but I am wondering if you are in a sense blocking towards those that are not right for you. SPeaking from my own personal experience, I have never been able to be intimate with someone I wasn't completely emotionally invested in i.e never did one night stands or random sex. The one "one night stand" I had, I ended up marrying her lol.

You are still young and you might just need to find that one special person that is able to open you up. The disinterest honestly sounds to me that mentally you arent ready for sex, and that is okay. Sex and intimacy should never be rushed. Hope this helps your some, and welcome to Psych Central!