Husband rejects sex post partum 9 months and cheats

Hello I am 9 months postpartum. I have had sex exactly once. Husband rejects me everytime I initiate. He says he is tired from work and just don’t have any energy for sex. He is a great dad and contributes a lot to the family and shares chores and helps most of the nights. But since the baby we have been having lots of fights and also we have zero help from either of the family. He keeps saying he wants to have sex and things will change soon. I asked him if he feel any medical problem but he said it’s just that he is not able to have sex with me. I feel really hurt but I am holding on to the hope that this is just a phase. My husband has been having more pressure from his family as his dad is sick and he has to drive back and forth an hour whenever his dad is sick and manage our house as well. Now he went on a business trip to Seattle and I found out that he started to flirt with some random girl from Chicago on Facebook and asked for her phone number and deleted the chat and also received an email saying he downloaded tinder. I asked him about tinder he just gave some stupid reason. He is still in Seattle. I am feeling like I am living in hell right now. I can’t imagine breaking this family. He is honestly such a good dad and he is loving to me, however things are not same before baby but he still tries things like cooking doing chores and says that this is the way I show my love. I am ok with that and even if the sex is just a phase I am ok to be patient but now he is upto something I don’t know what to do. I want honest opinion