I am trying to decide if I should stay in my almost 12 year marriage or walk away.

I have been married to a very respectful man for almost 12 years. He has helped raise my almost 13 year old son, we have had two kids of our own together, we recently adopted a 7 year old also. He has no motivation in life, no drive to push himself further in his career, doesn't like to be that active with our kids, doesn't enjoy learning new things, doesn't compliment me, doesn't try to think of the little things to put a spark in our marriage anymore, has allowed me to cheat on him, has gone out on his own with my permission and have extramarital affairs, I am not physically attracted to him anymore, and on the positive side, he is on his way home from a deployment he served to get us further in life, has allowed me to do surrogacy for other couples to help them make a family, helps at least 50% with housework, is very respectful, loves me unconditionally, has been fairly supportive over me being a stay at home mom and pursuing school and careers over the years, and he does love his kids.... Problem is I am not in love with him anymore, not sure I have ever been totally in love with him, more in love with the idea that he was so good to me. We have discussed divorce a lot over the years. Currently we are the furthest we have ever been in moving away from our marriage. With him deployed, I have been seeing someone for 7 months that I told him about and that relationship may be ending now. He has a weekend planned in a few weeks to meet up with a girl he used to go to high school with. She is flying in from Florida to be with him for a weekend. I am obviously upset over my 7 month relationship with a narcissistic man ending, worried about telling my kids about our seperation and I am not sure how I will financially make it with just a medical assisting career. My husband is willing to take care of me while I put myself through nursing school. My question is... should I attempt to try marriage counceling and try to fix what is left or walk away now since I obviously have taken the sanctity out of my marriage? he is willing to take me back... but I also think he needs to step back and take a look at what we have done to destroy our marriage and if he honestly thinks it's salvageable. I may never be able to feel the passion for him that a married couple should have. I am not sure I ever recall him and I having the passion I desire.