I second the books and thread that Losfer suggested.
But I am here to t/j this. When dealing with an addict the underlying addiction is the root of the infidelities. If that is not dealt with the risk of a relapse is not only probable, i believe it is inevitable. That relapse can be in the form of drugs, alcohol, other men, shopping, stealing or anything that feels good in the moment. I have BTDT for years. I wrote this in the I Can Relate thread R'ing with an addict.
Addiction is a disease that you can never fully understand unless you have it. Even therapists and councilors don't really get it.
Addiction is an obsessive/compulsive disorder, where the tick is self. Addicts cant think of anything, say anything, or do anything that doesn't revolve around themselves. They have a hole in there gut, or a sense of dis-ease, that there is something incomplete with them inside. They obsessively search for something that will fill that hole and make them complete: drugs, alcohol, sex, gambling, shopping, food, sports, work, money, you name it. These things work for a short period of time, then the guilt sets in and the hole grows. This is where the cycle of compulsion starts. "Whats next? I need more!!!"
Most addicts I know are sensitive, loving, caring people. They dont want to hurt anyone but that need to fill themselves and the guilt from doing it is so overpowering that they cant stop.
I have found freedom from this vicious cycle ONLY through vigilant 12 step work in a 12 step fellowship. My priorities in order are:
1. 12 Step Fellowship
In any other order I will eventually destroy everything around me.
I am also in a relationship with an addict. The last six years have been a cycle of relapses and A. For her the addiction was the reason (not excuse) for everything. That is her story and I will let her tell it. DDAY was Black Friday 2011 and TT until 9/11/12, when the whole truth came out.
We are in R. We are working vigilantly on R from many different angles. "THE DEAL BREAKER" for me would be lack of 12 step work on her part. If that stops so does the R. I know from my experience and the experience of many others, that It Works...
Feel free to PM me if you want.