For men, sex and love don't have to be one in the same. Sex and feelings don't have to be related. Sex is an act, an act some use to express love, but in nature it is just to promote reproduction and in society it is even an art to many; a profession to some and a casual hobby for others.
There is a reason your eggs are few in comparison to our millions of seeds, as men are meant to spread their seed, fertilize...etc etc...
None of that means you have to be ok with your husband wanting you to enter the cuckolding world. It doesn't mean he doesn't love you, he just loves you differently than you love him. His love isn't limited to sex and perhaps he just wishes to explore the relationship you two have. Afterall, is it not a purpose of marriage to grow together, whether it be spiritually or sexually. Don't do anything you feel ill about, but don't be afraid to try new things.
If there has ever been someone that has intrigued you sexually...this could be your opportunity to have your cake and eat it too.