I think it really depends on what you feel comfortable with, the way you speak about it, it seem that you see the cheating and the porn as the same thing. To me however - porn and masturbation is pretty harmless, while cheating will probably get me to pack my bags and leave.
I understand that the situation is complicated on account of your daughter, however, I think that the first thing you should ask yourself is "do I really want to be with this guy?" a lot of children go through their parents divorce and come out OK - I don't think that you having a child is a good enough reason to stay.
I also think you should ask yourself, why, aside of having a child who needs security in her life, you choose to stay in a relationship with a guy who's addicted to sex. What is it that the relationship, in it's current form gives you.
Sex addiction is a mental \ physical condition, it will not solve itself with just you getting upset and telling your partner that you are insulted by his behavior. Even ultimatum of leaving and so on, don't solve the problem - he probably have very little control over this. The only way to solve a sex addiction, as an other serious addiction is through therapy and maybe a 12 step program. If your partner is serious about getting over this problem, then he should start some from of therapy and work on getting rid of his addiction. If he's not serious about getting rid of the addiction, then basically, I think you should leave cause he's just going to go on with this.
In a later stage the two of you might consider couple therapy to try and restore the trust and intimacy that was taken away from the relationship by his sex addiction.
For more information about sex addiction and how to deal with it:
SAA (sex addict anonymous)
12 Questions - see if you have a problem
Sex addiction help