Help!

I caught my partner on a dating site, I'm so devastated I have never been this hurt in my life! I can't eat or sleep I couldn't even face work today! I don't know what to do! He says he never met anyone from it or he's never cheated on me with the app but isn't the app enough? I'm so confused I don't know what to do. The hardest part is that even tho he has done this to me I still want him because I love him! I have never loved anyone like I do him! Please talk some sense into me!