my heart goes out to you pal , i went through this too.

she would only let me see my son if i grovelled to her and as i didnt have parental responsibility at the time could do fek all about it.

spent thousands to get a defined contact order and she spend far more trying to stop me. the best advise that i got was to make sure to devote every second of every occasion that i was with him entirely to him - no phone calls to mates or anything which was not 100% for him. make him see the time you have together as special time. was great advise because it is difficult for anyone to do this full time (ie the ex 24/7) and meant that he was dying to see me - he would even ring me up when he learnt how to use the phone when she was in the shower. eventually she realised she was shooting herself in the foot and relented.

good luck