Unfortunately like in many korean dramas.. some guys will always be like this.. Even at a time when u needed them to be understanding the most. Some guys hates commitment and help up voluntarily when situation turns difficult.
So at this point u have urself (and of coz, us the TAP community as well) to put in the effort to get him drawn to u again.
Dont throw urself at him at this point. Dont offer to have sex. Make him come to u instead. Engage urself in something fun activities-ie join neighbourhood community, dress up more often, go out for tea time-bring ur baby etc and basically have fun with life and baby- independently. Have an ambience that is so inviting that even a tired person want to be with. It makes it more inviting.
If u are able to do that, it'll prove to him that spending time with u doesn't equivalent to just taking care of baby-feeding/bathing/changing diapers and ranting about baby& his parents but rather show how empowered u are being independent and take care of ur own baby and STILL be able to have fun whilst doing that.
And if u can, go ahead and dress up (even at home) and make urself attractive again. I understand how sometimes-when we r tired takin care of baby, we just wear casual and home clothes that makes us look like aunty.. so watch out for that as well. Buy few dresses online. Man loves fresh things. Sometimes we gotto be the feast to their eyes.. additionally, dressing up always boost our confident as well. So that's a bonus. : )
If he still does chat with the girl, then I can bet with u.. some time down the road, he will regret his a** for neglecting u like this. Stay strong, girl. U've got this.