Is it time to separate?

My husband and I have been together for 5 years and married for just over 2 of them. We have been through so much together and I am at a point now where I believe we need a break. We have a 3 year old daughter who we love dearly. It is for her sake that I am most hesitant to leave. Before we were married he cheated on me once and I only found out by finding the evidence in his phone. I thought all it would take would be one time but I forgave him. Since that time there has been numerous occassions of him talking to women; claiming he is single, and basically trying to sleep with them in the end if they will let him. I have found out about a good bit of these conversations but I still forgave him. Against my gut I married him and it wasn't even a month later where I found conversations on Myspace where he was downgrading me to a female and trying to get in her pants. That was the most hurtful thing because we hadn't even been married 2 months. With this same behavior going on I started to seek comfort in someone else and we ended up sleeping together. I would have never cheated on my husband but I felt like I was just. In actuality I was not better than he. I admitted my infidelity to him and we both cried and both decided to start fresh and forgive and move on together. He is a great dad and it breaks my heart to think how it would affect my daughter if we seperated. I recently found more conversations in his phone trying to hook up with other women. I didn't cry this time or confront him. I love him so much still but I can't keep living my life this way. I feel that he will never change. I don't want to hurt my daughter but I don't want to stay in a marriage where I am not happy. I need advice on what to do.....should we seperate or should I tough it out so my daughter won't be crushed? I have every intent on letting him see her; I would never deny him or her that.