First of all, I do hope that you’re using some other method of contraception now that you stopped using condoms, or else you’re both going to wind up with something else to worry about, an unintended pregnancy. Condoms do deaden the sensations somewhat, so the fact that you are no longer using them could have caused this premature ejaculation that you now have developed. But it could be something else as well. If one time you couldn’t last, and then worried that you’d have the same problem the next time, that could become a self-fulfilling promise. That you are having oral sex ahead of time shouldn’t be part of the problem, though if you can make your girlfriend sufficiently aroused via oral sex so that she’s just about ready to have an orgasm, then you might not need to last quite as long for her to get satisfaction out of intercourse.