My husband has been cheating on me. We have a baby. What should I do?

My husband and I have been together since college - for 13 years. Our daughter is 19 months old. When he was in Las Vegas with his mom and sister three weeks ago, he met some girl at the blackjack table after everyone was in bed, they got a room, and they have been calling, texting, emailing, and picture-mailing naked, y pictures right up until I caught him a week ago. His initial reaction was not to break it off, but to just say he was sorry followed by, "but we were miserable." He swore to me that they did not have - just (as if it matters). After talking to his family and thinking about things, he has now been very regretful, apologetic, and wanting me to try and make it work. We are both successful professionals with demanding jobs (ironically, I am a family lawyer), an upside down home, and a baby. We have no local family support. When our daughter was born, she had severe acid reflux and colic so she (and I) never slept. I developed PPD and when I was having panic attacks and on the verge of a breakdown, he was not supportive and told me I was making it all up for attention. I was crushed. When I returned for work, my employer was very flexible so I could leave in time to pick up my baby from daycare. Meanwhile, my husband was working late and I bore the brunt of taking care of the baby in addition to everything else. I was extremely resentful and was constantly angry with him, complaining he wasn't involved enough (our daughter had not bonded with him and always wanted me - not him), and criticized him. This would escalate into daily arguments over nothing. So, yes, we were miserable even before the affair. I still love him and he loves me, but is that enough? I feel like he didn't just betray me, but he also betrayed our family. He said he did it for the attention and excitement of it and because she was "nice" to him. She lives in another state, but the fact that he was carrying on like this under my nose at the same time we were attending therapy together, remodeling our house, and making future plans is even more deceitful. I should also add that when we were married for a couple years, before the baby, when I was going out with my girlfriends all the time, I kissed a guy at a bachelorette party and was emailing back and forth with some other guy who worked with my friend. He did not know, but in resopnse to me going out all the time and suspecting me cheating, he posted his profile on a and dating website and was chatting with women about . He used to smoke weed daily - even after the baby was born, and looks at internet and masturbates on a daily basis. I know this is a lot of information, but I am so lost, hurt, angry, and confused. I just need some neutral opinions here.