Gosh, that's a tough one. I don't think opening your marriage just so he can get some sex is the best idea... What have you done to increase your interest in sex? Some people do have low sex drives, and some are actually asexual.
Have you talked to a doctor? You might have a low thyroid issue happening. That can affect sex drive. Thyroid issues are quite common after pregnancy.
I had next to no sex drive while breastfeeding. But I think it was mostly exhaustion from caring for my kids. I had 3 kids in 5 yrs. My youngest breastfed til he was 4. When he was down to one nursing a day, and finally sleeping like a log all night, my sex drive came rushing back, like crazy! I've been making up for lost time ever since.
However, I had plenty of other parnters before I met my soon to be ex husband, and lots of sex drive before kids and finally, after. And since he and I broke up, lots more sexual exps as well. Missionary is delicious, but there is so much more out there.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags (poly, F, 61) loving miss pixi (poly, F, 39) since January 2009, living together since 2013
"Master," (mono, 34), miss pixi's Dom for 3 years