I feel really bad for you and your WH.
Not sure if the order is correct but your WH had some sort of an affair. Your baby passed away at almost fullterm. Your dad passed away. You say that no one is really there to support you in much of anything. You have a special needs child. You are in college working towards your masters degree. At least one of your kids is in a time consuming competitive sport. Sounds like your financial situation is tight. And I haven't read your back history enough but it also sounds like there is someone who is drinking heavily and getting drunk when you needed their help. Was that your mother in law that you were referring to? Oh and your mother in law is li ING with you also?
Of course you are tired and stressed out! Lots of stress! Stresses me out reading this!
You have A LOT, I mean A LOT on your plate! Makes my head spin! And although you weren't close to your dad, I'm pretty sure that there is some sort of grieving going on. And the loss of your baby definitely took a hit on you and your marriage. And your WH destroyed your trust. And I also get the feeling that he may think that you are punishing him for anything and EVERYTHING?
This is just my opinion but I think that something needs to give in order for you to figure yourself and your life out. And grieve! Grieve your father's death, grieve the baby's death, grieve the loss of innocence and trust in your marriage. You lost the ability to lean on the person you trusted most when he stepped away from your marriage and gave his attention to another women.
I'm not sure if your marriage is dead but I surely can tell you what would benefit you and your WH is to work on a plan to slow everything down so that you can think!!
I honestly believe that your WH is crying out for help and you can't hear him (and he no longer can hear you!). I can see that you are crying out for help also but no one can hear you either. And everything now has turned into conflict. And what would your WH say if he came onto this site on the wayward side. Your marriage is in trouble!! But also understand that your WH affair is 100% on him. He chose to seek someone else out to comfort him.
As you stated and from what I've skimmed over is that you want to save this marriage? So what can you do to start the healing process in the right direction? It isn't about sex, it goes way deeper than that. The two of you are crying out for help and neither of you can hear each other and I can totally see why.
I believe that the two of you have poor coping skills and where you are at today is the result of how each of you have coped throughout all of your losses and in daily life itself,imo.
I am sorry for all of yours AND your WH's losses and trauma. Dealing with it head on is your best bet. Sweeping everything under the rug is just going to make life worse.
Keep posting here and hopefully you are your WH can try and work towards healthy healing and healthy solutions. Maybe get some IC and marriage counseling? Grief counseling?
I honestly believe that your marriage can be saved but it will take some hard work and change from the both of you.