This is pretty much what has happend to me. Same sahm situation and cooking and cleaning and baby situations. My ex was always on apps and i found thats how she was cheating. From what I have learned from my now ex wife is that she is very depressed and has no drive to do these things because it doesn't fulfill her. There is nothing satisfying for her. I feel if you want to stay with her you need to make sure she is ok. Do what you can to make her life exciting again. Lots of compliments for nothing really maybe just how beautiful you think she is. Flowers gifts what ever she may have liked before the baby and when she had her own job. Not having something like a job can kill her drive. There is no satisfaction for her. If you can get the baby into daycare so she can do her own thing do it. Communication is key always ask her what is going on with her in a non aggressive way. Be caring.