Is he a cheating arse wipe?

Sooo I decided to look through my partners phone, I never do this just felt like he was hiding something, I have been with him nearly 4 years, we are engaged,our own home and have a 2 year old. So I found a few messages from other women on his phone one was a 51 year old woman, he is 24. He told her he was engaged and she said so was she, they started sending dirty pictures to each other and saying sorry things, I was angry by now felt like punching him in face. I started reading another message from another woman, this one made me cry I felt physically sick, the more I read the worse I got,me and him had a break of 3 days about 19 months ago, at this point he started messaging her so 19 months ago go they have known each other, she new all about me and our son, he's told me nothing about her, she asked questions about me even looked me up on fb a few times, he seemed to not be too bothered but she was messaging him with sexual messages and dirty pictures, now she's had a baby on the past 2 weeks and messaged him almost straight away to tell him she had him. I have no idea what to do :( how do I confront him? Do I confront this woman I think is a dirty home wrecker? What am I supposed to say? I love him with my whole heart but I don't want to go threw this:(

(Schmokinnnnn-Hot Susie!... I have absolutely utterly (for once) nothing to add.) (More like her, please, Bartender!)