I think that the way I masturbate is affecting my ability to orgasm with women.

I am circumcised, 22 years old, and have had just 3 partners that I have gone all the way with. None of them have been able to come all that close to making me orgasm in any way other than penetration. We tried many methods, and they all expressed the fact that were able to make other partners finish with these methods relatively easily.

When I masturbate, I almost always use the same method. My right hand stimulates the glans (using just my thumb and first two fingers -- not the fist), while my left hand stimulates the base of my penis through the scrotum. The latter is absolutely crucial to getting me to a point where I feel like I may cum soon, and is also something girls have not been able to reproduce. I also masturbate to porn on occasion, though it is not necessary for me.

During intercourse, I can usually finish, but that all depends on the position. In missionary I find it quite easy, because I am able go deeper. Girl on top works sometimes, too, but all others are either very difficult or seemingly impossible. Being able to go as deep as possible seems to be a necessity with me. Some positions, like spooning, I find very difficult to maintain an erection during, particularly if I have a condom on. There have been times in the past where I have not been able to finish with a condom on, and have had to take to it off and masturbate in the end.

Note that I also masturbate quite frequently, and the whole problem could possibly be due simply to this. I have gone through the majority of my adolescent and young-adult life 2 to 7+ times per week.

Has anyone else ever had a similar problem? Any suggestions?

I don't ejaculate at all.
I personally it may be more because of the frequency rather than the method you're using, cut it right down.

REALLY try and only masturbate once a week and when you do make it worth it, bring out all the stops, the lube, favourite porn, the works.

You'll save time rather than the whole x7 a week and would expect it would help in the bedroom.

I need to follow this same advice really

I'll try that for a few weeks; hopefully that will help out.