Aw my! this sounds exactly what I and dh went through until a few months ago.
We have two kids below 2 (twins) and life wasnt that fantastic at all. DH made enough money and so I became SAHM, going through a twin pregnancy almost destroyed my shape. I constantly complained that he didnt help around the house much and cant wait for him to come home and take over the kids for an hour atleast.
For me it was physically & emotionally very draining, I had to take quick showers and pull up my hair, hardly get time to look at the mirror and when i get to look at one, I felt like not doing it again
DH started to look at pretty women even when i m around. I became jeolous, quarelled with him, he became distant and all these lead us to live a non romantic life (sex was still on the plate on and off for pure physical desire).
Now things have changed a lot, I have got a full time maid to help me with all the household chores, I give myself once a week to catch up with my friends who are working so that i can keep up with the trend, I get to go for spa, pedicure etc. Oh most importantly DH gave me a shopping voucher from a famous sports shop and gave me good $$ to use up for my fitness program. I feel great now (though not completely in shape yet). I have once a week aerobics class, yoga, I jog 3x a week and have a very active outdoor life together with my kids.
What made me change? When he gave me the voucher and $$ I knew he wants me to be back in shape, I knew that his eyes have been wandering lately, I knew that he loves me and the kids a lot and will do anything for us and I knew that I want our happiness back. Oh forgot to mention, when he gave me the voucher he had a card with it written "I want my wife back, please come back" to me i felt that this was touching and emotional.
Besides the above mentioned reasons, I want to be a role model to our kids and introduce them to fitness activities from young.
Sorry for the long post, just wanted to help by sharing my story as it seemed to be similar to yours. ALL THE BEST