Possibility future divorce, I have 2 boys not from this marriage, how should I handle this divorce?

Explain further: I am remarried, of 3 yrs to someone who is a good guy that has not learned to stop making bad choices all the time in our marriage. I am exhausted, I have done everything that I can to try and save this marriage, it's not working, I guess some marriages are not meant to be saved. Anyway, I have 2 boys not of the marriage, a 13 yr old who can careless if we get divorced and an 8 yr old that calls him "daddy"; they both know there fathers. Although they both live in Fl and I am in Mn. I'm ready to move on, as a matter of fact I'm putting everything into place to move on and get a separation and the strong possibility of divorce. The thing that makes me worried is my 8 yr old. He loves this guy, I do too, but i am not in love with him, anyway how should I handle this with my child. It's not the same as getting a divorce from the father of your kid, this is different, he would have "no legal rights" to them, I honestly dont even know if he would after a while stay in contact with them after our divorce. How should I treat this with my son. It's bad enough my son barely has a relationship with his father and this guy has been the closest thing he has to a Dad.. this breaks my heart. Such a stupid woman that I am to allow these men to hurt us... please any advise?