Hi, before anyone can answer this I believe you need to know the history. To summarise it all the first four years were normal. We had stupid arguments in which we'll over react about and then make up.

We ended up going on a wonderful holiday and produced the best little midget in the world (not really a midget, but one of the greatest things to ever happen to me.) just before the birth of him I got cold feet and nearly bottled it... I ended up giving this other girl a smooch on the neck and trying to always be faithful told my partner everything
She was obviously hurt from this and we managed to work it out.

Recently we went threw another bad patch. Hoping to nip it in the butt before it got out of hand, we decided we'll do some couple counseling. Before we could even go to a class, I seen us getting worse. Then came a night where she was going out with her high school friends, and I got that gut feeling that she'll end up doing something stupid. But I was unable to stop her from going out.

So she ended going out and she made out with some guy. Usually I'm the guy to be pissed off and get stupidly angry. But the thought of 'us' being over destroyed me. I was extremely depressed for a month or so. In the meantime I got very jealous and I wanted to know everything. I contacted the guy and got more information... Turns out this guy knows some people that I know. So she was the one that came on to him... And she told me herself that her friends were like 'wow well done you've pulled'

In the mean time even though knowing all this I'm still wanting to try make things work. Not just because we have a little boy together but because I want to.

But since being together I have found that she has been keeping things from me, she'll lie about small things and I even caught her checking out other guys in front of me. This makes me feel angry/upset/depressed and empty all at the same time and I'll have to shut myself off and makes me react erratically like taking pictures down and puttin them out of sight.

What should I do?

It's not enough for one person to try to make it work. You both have to do it. You both have to talk about what you want from the other, and give it to the other. Have you considered seeing a couples' therapist about it?

From what I can see it seems like you two lack healthy communication. If you are serious about wanting to fix the relationship and stay together, then you both need to go to couple's therapy.

While there, you need to set clear boundaries about what's appropriate and what isn't. If she can't check out other guys in front of you, she needs to know that. You both need to work on loyalty, and that probably means stop putting yourselves in situations where you're liable to cheat.

The most important thing that you two need to figure out is if you're both in this relationship. No need to work hard at fixing something if you're not both committed to it. Definitely seek couple's therapy as you mentioned and communicate expectations and boundaries.

You're parents and your responsibilities towards your child must come first.

You should definitely go back to couple's therapy.

This is a good time to back up. And re evaluate this relationship, as honestly, I would focus on being the best dad I could be without having a romantic relationship with his mother. Sure we could talk, and plan for the child, but would have nothing if little to do with wasting time trying to building a future with someone who obviously wasn't ready for it. That's just me though.