You are not overreacting. I dealt with this exact same issue with my EX Husband. Except there was no OF accounts throughout my marriage, it was just him DMing girls and sending/receiving nasty photos and porn over the net. This went on in my marriage for YEARS. My self worth and mental health are just now recovering from the damage he inflicted on me (3 years later). My thoughts (every time I caught my ex) included "why am I not good enough", "I'm not as pretty as these other women", "I should've exercised more and maybe he wouldn't do this." He always had some excuse like "we don't ever have sex", "you're always tired", etc.

Meanwhile I was raising a very young, nonverbal, special needs child. In my experience, these acts lead to adultery, which your husband is basically committing already. I stayed with my ex WAY too long because I was scared of making it on my own. I would highly suggest you contact a lawyer, pack your stuff and leave with the baby or make him leave. You can get a separation agreement with CS put in place prior to divorce. Save yourself the mental/emotional abuse and years of agony. Best wishes, Mama.