Masturbation/sex/cumming

Does anyone else have trouble cumming?? I just can't seem to let go, I can be feeling absolutely amazing during sex or masturbation but it feels so intense that I stop if I'm masturbating and they tend to finish before I can and I don't tell them that I haven't finished cause it's just something I haven't done - any suggestions to help?? Please?? I can be screaming from how good the sex is and still not finish and it's getting frustrating