I was there from day one with my son. Was single when I impregnated his mom, got with her four months after he was born (for 4 years). When we split up she let me see him once a week then decided to move without saying where and changing number.
It was horrible. I didn't get to speak to him on my birthday, she started dating a guy from England and I worried she'd move. My mom parents were too soft and thought things would work out but I instigated legal proceedings for custody.* I had her bring up loads of shite in court but got custody and legal guardianship in the end. She accused me of drug dealing, hiding cocaine in his bed etc, all lies but judge gave me custody and guardianship and access.
We get on great now, it took a year or two but she eventually saw that he has tp be put first. She is happy with her now husband, I am happy with my girlfriend. I can see him when I want, he loves me he loves his mom and his step dad. It was tough as hell, suicide contemplating tough, but I'm here now and he's the happiest kid you could meet.
*On the issue of custody, I see him every Saturday as per court agreement but more often most weeks when I have time off or if he is on holidays from school.