The past can be a painful thing to deal with but you have to remember that forgiveness is more for YOU than the other person. Part of forgiveness is FORGETTING the past during arguments. Think of yourself. Everyone has skeletons in their closet and if you're in an argument with someone, you don't want them throwing that stuff in their face. That's called bitterness. You don't want to be around bitter people, so you have to choose not to be bitter yourself.
YES, I have been through it. So much more than I care to share on a public forum anymore, but trust me when I tell you, you're not doing yourself or the relationship any favors by holding on to this grudge. Any infidelity before you chose to be exclusive with one another-doesn't really count as infidelity now, does it? If my relationship, which has been understood to be exclusive for 14+ years can survive what we went through because of choices he made, if you two really want this relationship, yours can as well.
Suffice to say, that the biggest tip I have for you is forgive and forgive wholly.