M.S.
Since we don't know anything about his father, it's hard to say. I don't want to scare you, but I wouldn't force your son to go to his dads. Follow your gut until you find out exactly what is going on because it definitely sounds like something more than being just bored. I am not saying this is going on, but I was sexually abused by two older cousins when I was around 3 or 4 yrs old. I recall telling my mom I was sick just to get out of not going to their home. I also became overally sexual at a young age. It took me years to finally tell my mom and I sought counsling. I urge you to listen to your instincts. I don't think I would ask his father yet...try to get it out of your son. Make sure your son knows you aren't mad at him and that you won't force him to go to his dad's and see if his mood changes any.