Any possibility of HIM finding an additional partner.
While I will echo everyone else, and say he does sound rather self-focused and less caring about YOUR feelings, then I personally would want in a partner, one of the advantages (imo at least) of a Poly life style, is the recognition that a relationship can be 'good' but not everything a person needs.
If you have a cuddle-buddy to fulfill your needs, would you be ok, if you husband got a hump-like-a-rabbit buddy to fulfill his needs.
I would try to talk to your husband and explain.
1) Making you dislike/not look forward to sex with him, is NOT going to increase your endurance, but make you like it even less/want it less. You certainly can 'increase' your endurance, but more then straight sex, its about build-up, and not quiet letting you hit the peak. The trick is you need to ENJOY whats going on, for as long as possible... Straight sex, is less likely to extend that then, hands, fingers, toys, tongues things that can be lubricated if needed, and easy to push you to the edge, but not over and hold you there... so yes you can build endurance but doesn't sound like he is going about it the right way...
2) Now It does sound like you have somebody you can get something you are needing but not getting enough of (cuddle time), but does sound like your husband also is missing out on something. Would you (and/or him) consider a partner for HIM?