I think your subject line says this plainly enough. What type of custody arrangments do you have now? I assume from what you wrote that there is no male figure in your son’s life?
My ex had a similar situation with his son, from his first marriage, and I can tell you that he was about the same type of father that you say your ex is. He got him occasionally for a couple hours when we first started dating and eventually started getting him every other weekend. He was about 8 or 9 at that time. When he was 11 he decided he didn’t like his new stepfather and decided to move in with his dad, my ex. He never had rules, chores or responsibility at our house. It was always playtime. I didn’t have ANY say in this, his father made that clear. He told me that since I was not a mother that my opinion of children needing boundaries and guidelines, didn’t mean squat to him. One of the reasons he’s my ex. Anyway, eventually this backfired on him. After he and I split up, he remarried and about 6 months later his son decided to move back to his mother’s, that was about age 15. He was not doing well in school, and was starting to run with the “wrong” crowd, and with no discipline he wasn’t going to get any better. It was his choice to move back to his mother’s.
That being said, your ex may be ready to handle the responsibility of nurturing a relationship with his son and teaching him morals and values. He may be able to give him guidelines and boundaries. You have to question whether it is worth finding out the hard way if he is. If there is no custody order in place as of yet, I would tell you to sit your son down and tell him why you will not let him live with his father. That you are not keeping him from his dad and he can visit any time that will not interfere with school. You will be the bad guy. Let’s face it though, teenager’s are not known for their emotional stability, and no matter which decision you make you will likely lose your son emotionally to some extent with him being 13.
If his father wants this badly enough, he will fight for custody. It will then be up to him to prove to the judge that, after 6 years of minimal contact and involvement, he would be able to provide a better life for his son than what you have. Hope you have kept some sort of records.
Your son does not need a “man” in his life, he needs his father. He needs both of you but it sounds as if it’s only just now convenient for your ex to be there. Though it’s never too late to start being a good parent, in my opinion, after 6 years, it’s not fair to you or your son to say “I’ll take over now”. In my opinion, this will make the hardest years of life (teenage years) even more unstable and emotional. Fight for your son, not against your ex, and explain that you think this is what’s best. Hopefully, down the road, your son will agree and thank you.