Unfortunately, I have to agree with 1Faith. Many of us here at SI, like me, have the option to leave our betrayers. We stay, though, for many reasons--primarily marriage vows (important to us even if not to them) and children.
I love my WH desperately and unconditionally. That said, the only reason I'm still with him after finding out about his affair is because of our 22 years together and our 4 children. If I were unencumbered by those realities, I'd be gone--especially after reading what I've read on SI.
If your boyfriend, IMO, can't be faithful to you without the pressures of children and marriage, he won't be faithful to you later. Many of us found out "too late" so to speak. You've been given a gift to know now, before you've legally committed, before you've created new life together, what your loved one's character truly is.
I believe in forgiveness, I believe in repentance, I believe in change. I'm proof of that. Perhaps this could be a time for you to explore what drew you to someone who could be unfaithful, what you did that contributed to the breakdown of your relationship (not the affair--that was his choice), and what you will do to make your next relationship more healthy.
And, yes, I think you should break this one off and look for the next. Your, in my mind, soon-to-be-ex-boyfriend can use this experience as something that will change him for the better and prepare him to show his next significant other more fidelity. That's what life is all about--using challenges and struggles to become stronger and deeper as individuals.
Regardless of what you decide--to stay or go--we'll all support you and help you. The pain of betrayal stings and scars everyone in a somewhat similar fashion. We are all wishing this not-so-exclusive club didn't drag us--kicking and screaming--into it. Wouldn't it be nice to find out it was all a huge mistake and our membership cards could be rescinded?