It really depends, 8x8,

By "sex," I assume you mean intercourse? In that case, the issue may be the condom you're using. Try a thinner style. In addition, the start-stop-start coital patterning is often use to PROLONG the sex act, particularly for those who experience premature ejaculation. So if you've been doing the off-on-off thing, then yes, it could conceivably take an hour or more prior to ejaculation, thereby rendering the penis more insensitive.

I'm just curious to know what happens if you go full speed ahead and don't interrupt anything once you're in there? Sensitivity is often related to the time it takes to ejaculate, i.e. a really sensate penis will ejaculate quicker than a penis experiencing reduced sensitivity.

Other ways of increasing sensitivity is to get some BBBJ, but that's not on the menu for those who are risk-averse. Needless to say, the more you play condom-less, the more you'll feel, although that should NOT be taken as an endorsement to go out there and have risky sex. But manual stimulation without a condom does carry a fairly low risk, so you may start with that.

And of course, there's the issue of preference. While some love to get bare hand and oral jobs and finally stick it in with a condom on, go at it and then explode, others like to go back and forth for quite some time with the penis encased in the condom for the duration.

Sometimes doing male Kegels, i.e. strengthening the PC muscles will increase orgasmic potential. As to specific sensitivity, the condom is a barrier no matter what. Try to experiment, everyone's different in this regard.

Good luck,
the Love Goddess