Husband doesnt want sex

This is going to be a lengthy post so please bear with me. We have married for 3 years, we have a child and we are in our late 20s. Before we got married, he used to be horny for me all the time. We would do it about 3-4 times a week, we would play roles and sex games. Whenever he wanted it I'd be up for and vice versa. Until we got married! I remember in the first four months of our marriage we went a whole week with him kissing me, I talked to him about it and he would start kissing me on my cheeks. He didn't cuddle me either and when I'd ask him to he'd say he is tired. The frequency of sex went down to about 3-4 times a month. We got pregnant and sex stopped, he said he found it weird to have sex while I was pregnant, granted, so I offered him blowjobs as well, he turned those turned too. After giving birth it has dwindled down to once in two months, I talked to about it and it went up to once a month, it still wasn't enough for me so now it's it twice a month IF IM LUCKY. His main excuses are that he works 8 hours a day and he gets tired but funny enough in the past two years he found a "hobby" which he is never too busy for and which he spends an additional 2-3 hours with after work, every day!! He has admitted to watching porn and jerking off several times a week. Which hurts even more that he does that when he knows I'm willing to have sex with him. I won't lie, I have thought of leaving him, I am too young for this!

Oh and a little prehistory: a few weeks after our wedding I found text messages to his ex and he was asking questions about how she keeps her sex life exciting and him criticizing my body. His ex is a pole dancer and I found videos of her dancing on a pole in their message thread. He even went to one of her shows while we were in our boyfriend/girlfriend. He maintains that they are just friends but I think he might still have feelings for her. I am just tired of this. In the beginning of our relationship he went on a site and he discussed his sexual fantasies with a bunch of girls ( but I only found out much later, too late if you ask me)
What could be wrong? Is this normal that sex in marriage declines like this? This early?
I am sorry for the vent and the possible grammatical errors. As I write, I am almost close to tears