I am finally admitting it out loud.
I agree with the previous poster. And maybe it's just because I've just found out in the past few days that my husband is a totally different man. But I would get some real proof.
You could get a nanny cam or a voice recorder. The recorder might be cheaper and if they are having an affair you might not want to SEE what's going on. It might be a tiny bit better if you just heard it and you'd still know for sure what you were dealing with. (I couldn't imagine having to watch my husband! It would hurt exactly worse to have to see him.)
I'm sorry you're going through this. My heart goes out to you. I know the feeling when the tears start to fall and you wonder how you've still got enough strength to cry.