Whore keep texting my husband

Okay my husband and I have been married together for 4 years in July of this year coming up soon. We just have our daughter born last year. She is 5 months old. I met ex girlfriend at our wedding when we was shaking people hands and he told me who she was. It felt like a slap in the face. But making the story short I was about to put our daughter to bed and I used his tablet to play her Lullaby music. But as soon I open his tablet I saw his ex girlfriend and that he been contact her during our marriage. I was so pissed that I want to fight my husband. I asked him for marriage counselor but he think I’m am the problem. I want to file for divorce or go over her house and beat her ass but then it won’t be any better. And that is not the roll model I wanted my daughter. What should I do? And where to start?