Okay, sorry for the delay. Here's my experience with guys that have difficulty cumming during sex.
One cause can be their masturbation technique. Some guys maintain a death grip on their cocks while getting off. Now, unless you've been lifting weights with your vag, I doubt you can match this sensation. Solution would be to stop masturbating or change it drastically, have only sex or lighter stimulation. Basically, retrain the body to cum for sensations other than the death grip.
For guys that have issues with condoms, try masturbating with a condom on, and also putting the condom on a good amount of time before penetration when having sex. This will allow the body to adjust to the decrease in sensation from a condom.
Another guy I dated, said that orgasm was an intensely private thing for him. As a kid/teenager, his parents were very demanding of him, judgemental, and so he had some shame issues to deal with. For those who are "embarrassed" or self conscious about cumming, Dan Savage offers great advice, which I'll do my best to sum up. Basically, he starts by blindfolding you, giving you headphones and music to drown out his fapping, and even duct taping your mouth closed as needed.
He also wears a blindfold, whatever is needed to feel most private to him. As he gets comfy getting off like this, gradually the sensory-depriving items are removed, until he's able to cum with you watching, or participating with, etc. And you just build from there. The key is to go slowly, and not be afraid to back up a step or two when you need to.
This particular gent I was with also had a death grip, so there was plenty to work on! It was about ... 4 or 5 months into our relationship before he came during sex. He had had previous girlfriends who were not very understanding at all; he described it as feeling like he had to cum to save the relationship. Or, they would get off and not care about getting him off. We just took it really easy, I did my very best to never pressure him; as long as sex had been enjoyable and he felt satisfied, that was enough for me. If he couldn't cum after sex, it was no big deal, we moved on. It also helped him that I had difficulty cumming (meds and my own anxiety), so often neither of us came!
I think in general, society takes the male orgasm for granted. Sorting this kind of thing out is about separating your own issues (i.e. insecurity if he doesn't cum) from his (embarrassment, death grip, etc.). He also needs to want to "fix" the issue. If it's not a problem for him, then that's just something you need to accept.
Phew! That's my spiel.
Hope it's helpful!