lee i already suggested you go to the families need fathers website for further help. Don't expect them to tell you what you want to hear either though, they'll pretty much tell you how it is and if you're being unreasonable. They'll also give you support, advice and legal help if you need it and listen and accept it from them.
No-one likes it when they find out about the realities of the court route and how powerless you can be. Is it any wonder when it's all behind closed doors and you don't find out the realities of it until you experience it yourself. Up till then you believe that courts and judges make the right decisions. And then you're in it and you can't honestly believe the decisions made behind closed doors.
I haven't even mentioned to you yet the possibility that she could accuse you of DV and even of assaulting your child if she feels so vendictive. In fact she may feel threatened by you if you turn up unannounced or demand to know wbout your ds's welfare. Which you are entitled to of course, but it's how you go about it and how she's sees and feels about the way you go about it.
Believe me when I say I know how it can be for a father trying his best to see his child in the face of a mother who is determined to do everything she can to stop it. My last partners ex was such a woman. Her hatred knew no bounds and she swore blind to him he would never get to see his child. He did the court thing, followed the rules, eventually after a lot of money and heartache got a reasonable contact agreement after some 2 years. She then accused him of sexually assaulting his dd, envolved the police, her school and ss. And when that failed to get her desired result she kidnapped their child abroad and has been missing with dd for some 18 months now.
Or I could tell you about my neighbours ex. He has custody of their 2dc after a lengthy and traumatic court case. He said in court he would ensure contact with mother etc. But as soon as he got residency he suddenly couldn't afford the travel costs, would cancel at last minute, no car or had a puncture etc. He then called ss on her saying her & her mother saying her mother had beaten children with wooden spoon simply to avoid contact and she had to stay away while investigated - nothing in it of course but they have to follow their rules. He tried to get ss to take away her baby with new partner but failed in that thank goodness. And in court they said that they needed to let things settle and didn't think it was good to move the children back so soon after they had gone to dad. Now it seems likely that oldest dd is coming back to her mum of her own decision.
So yes it is awful what some parents will do. And it's awful what some parents will say and do and attempt to get away with.
The way you feel about your relationship and the way she feels is clearly different. You were ready to move on and realised it was over. She is not at that point yet and is going to take a long time to get there with the added pain and anger she is most likely feeling. People don't act reasonably or rationally when they are suffering trauma like this. In time things may be better, but they may not. Things may get worse if you go to court, or it may be the only way to get reasonable contact with your son.
But you have to stop thinking about what you believe to be reasonable and start listening to the realities of what you are likely to get and what everyone else considers reasonable. The vast majority of cases that go to court are likely to end up with every other weekend and half the school holidays. By the time you get to that in court your ds will be at school so your dream of 3 weekends in 4 isn't likely to be a reality I'm afraid. But I am happy to wait to be proved otherwise if you can get it.
Try here for more advice from people in your situation
www.fnf.org.uk/
and here
www.spig.clara.net/