Please help me with what to say

I was getting a room ready for our nursery and was going through some old mail. I fond my boyfriend of what will be 6 yes in August. We have a little girl and another baby on the way. I found his writing on a torn trash envelope and it had a website for sex dating and a password. He’s away at school for his annual test he’s required to have won’t b back till Thursday. I texted him this convo. He doesn’t get out till 5:30. It’s 5 now. I went behind him and checked his email witch I’ve never done b4! And he has spam and messages and other names he’s logged into all about sex! I don’t know what to do I feel so betrayed! Watching porn is one thing but if he’s been hooking up that’s a game changer for me!! Idc how long it’s been! What do I say should I just let him explain!! I’m shaking with hurt and frustration!!😤🤯🤬😡😠😱😢😥🤢🤮