Honestly do not know what to do!!!

My fiance and I have been together for over 7 years. We have had our share of ups and downs, but we managed to get through them...so I thought.

Recently, he has been treating me not in a very nice way and we have been constantly arguing. He has even been talking to his coworkers about our problems. All of a sudden he comes to me saying he needs some space, and to figure out if he wants to be in this relationship. We do have a child together and I have another child from a previous relationship.

After doing some talking, he decides he will stay to see if things work out, but he needed to confess something to me. He told me years ago when him and I started dating, he cheated on me with a married woman. We were going through some problems then and she was having problems with her husband. They worked at the same place then, so they became close. He would go to her house while I was attending school. He said it only happened twice, and then they both realized it was a mistake.

Now, he figures I should either still work on our relationship or leave him. Others have told me since it happened so long ago to just forgive him and work on the relationship, especially for the kids sake. I'm still in shock and can only think of him and her when I see him. I really don't know what to do.