Sometimes I try hard, sometimes I don't. We try all kinds of things but nothing works, although we make love for many hours. I can make an orgasm by masturbating. If you place your finger just inside your nice girl's vagina and ask her to squeeze, you will probably feel her vaginal muscles tighten. It is not clear to Alice if her vagina could be tighter, or if you have unrealistic expectations.
Few vaginas can grab onto a penis as strongly as one's own hand.
If this is the case, you can teach yourself to masturbate using a looser grip. Changing your self-pleasuring patterns can help you learn to respond to different stimuli so that you increase your own opportunities for enjoying sex with others. Being a good lover takes time, patience, trust, talking, listening, and practice. Truthfulness and authenticity also play an important part, since sexuality and intimacy involve more than sex itself. Because you orgasm with masturbation, it certainly doesn't sound like your difficulties reaching orgasm while inside your partner are caused by any physical problems.