My 12 year old son went to live with his father and girlfriend over a year ago. Residency was sought and won by his father. I have 2 children from my current relationship. My sons father live somes distance from me and my son has recently said that his is bored here and that I don't listen to him and that he does not like my partner.. we have been together for 6 years. The courts gave me contact every other weekend and 2/3rds of school holidays. My ex husband has always done everything to encourage my son to stay with him and won't even discuss his school choices with me. I firmly believe that I am trying to be alienated from my son. Any ideas has to how to get my son closer to me. My two other children are so upset as they have not seen him for several weeks.
My ex says I need to treat my son like an adult and let him decide when to visit.

Your son may respect you more right now if you treated him as an adult, but he is still a child, and later in life will look back, and possibly feel that you weren't being a "parent". This is a very difficult situation you are in right now.
You have visitations with your son, ordered by the court. Be sure to make those visitations. If you can't, then be sure to let your ex and your son know ASAP, and write down date, time, and explanation, and put it in a file. Keep all paper work, and if your ex winds up not abiding by court then you should be able to file contempt charges. Not that this will get much done, but perhaps deter him from doing it again. With that being said, make sure you are not "talking down" about his father in front of him, or the other children, as it will get back to your son. Your ex should be just as respectful, and if you find out otherwise, I'd take his a** back to court for slander in a custody case. Judges DO NOT like this at all
Good luck