What should i do about my son?

I'll try to make this as short as i can. Me and my ex have a 7 year old son together. We never were married and have never done custody matters in court. I just got Married about 2 months ago and my ex has a huge problem with my husband (they were friends in the past) and he tries to make my life a living you know what! Anyway, my son ask could he go stay with his dad, I hesitated but agreed to do so seeing it is summer vacation. Now that he has went to his fathers house my ex is refusing to let him come back. My ex states that my son "claims" that me and my husband argue,he does not like what we eat here (b/c i don't keep a bunch of unhealthy food around),he cant get on the computer and says he does not want to come back, My son has told a few lies to my ex so that he can stay with his dad longer (thinking he has it better over there BECAUSE his dad is buying his love and filling his head with stuff) and now it makes me and my husband look bad! When the Lord above knows he is not mistreated over here at all! and me and my husband do not argue around him,My son has always lived with me and his dad has been in and out of his life...I cant even get him to pay child support. I'm just not real sure what i should do. I mean if my son says he does not want to come back should I show him "tough love" and let him find out for himself how good he really does have it over here, seeing his dad don't even have his own place and stays with his mama? He has his own room here and anything he would ever need... i know his dad will not let anything happen to him but I still miss him. And I don't want my son lying on me and my husband just so he can get his way! That will cause nothing but problems, I'm so confused and have no idea what to do any insight on this matter of mine would be really great thanks so much!