Don’t entertain any of her petty games and always try to remain calm.
My ex ran off with my 2 year old son Harry. 6 weeks after, I found that she’d left me because she’d been sleeping with my supervisor from work.
I lost everything and even now I don’t get to see my son.
18 months on, and I can honestly say that I feel better without her in my life. Miss my little boy like crazy, but I know that she’ll make things as hard as possible for me to see him.
Like you, I don’t have the money for expensive court battles etc and I believe that he’ll come to me when he’s older.
First port of call is get down to Citizens Advice… and maybe go speak to a solicitor.
Good luck and keep your chin up.