I will say this once only, its not a case of if, but when he cheats on you again, their is no way you could trust him, especially the woman in question being his babys mother.
Look at her view, she sleeps with your boyfriend by clicking her fingers, she will use every trick in the book to ruin your relationship with him, tho it dosen't look to difficult a job to persuade him, i'm not the forgiven type in things like this, i've been married 16 years, and if my wife or me cheated, its over, trust is the biggest part of any relationship, if theirs no trust, its pointless continuing in a relationship, hes got the best of both worlds in his eyes, i admire your stance on sticking by him, but i've seen it all to many times with friends relationships in the past, the odds are against yours surviving unless you forgive him again, again & again.
Think what you are doing, no ones saying you don't love him etc, but for him to cheat on you, then ask for forgiveness is pathetic, its only a matter of time before he does it again, you will always have doubt in your mind, even if he dosen't cheat again, and whilst you have these doubts, i'm afraid yout relationship is not going to work
Its obviously your call at the end of the day, i hope all works out for you whatever path you take, you don't deserve this, their are many more fish in the sea so to speak, go catch yourself another one.
Good luck