Custody questions, do I have a chance to get it?

Okay...i'm a young father i'm 22 years old, I have a son who is 2 years old. I've had him on and off for his entire lifetime, his mother who is younger than I am has just recently had another child. When my son was around 1 year old his mother moved away with him to a different state. Since I dont' have anything established through the court besides Dna evidence that I am the father to see my son I have drove 8 hours everytime I wanted to see him to get him...and they have never even gave effort to drive to meet me anywhere sooner I always drove to get him. A year ago I was told by a group of indivduals that she moved back down here close to where I used to live but my son still stayed with the grandparents. I wanted to do something but she always said that she was "still there" when she wasn't. Even in conversation once before she moved down the first time she told me that if she moved back in with her boyfriend that she would just sign away custody to me...I mean to me alone thats enough. In one situation when I took him to see his mother her new boyfriend upon the first time meeting me he took off his shirt and inflicted damage upon my vehicle and tryed to come at me with my son in my arms. I talked to the Da and had stuff done about it but nothing ever went through. He was charged with damage to my vehicle of course, ault, but we couldn't get wanted endangerment over my son. He was never caught. 5 months ago my son moved back down here to stay. Out of these 5 months his mother has seen him in total...no more than a month. I've went a whole month without her even seeing our son. And most of the time he doesn't even stay the night he just goes up there to stay. But yet still every month I pay child support...when all of this money could be goin into actually buying him more stuff and getting him more of what he wants and needs. My son loves staying with me, he doesn't want to stay with her...he refuses in fact. I love my son more than anything in this world and I really don't know what to do...and I really want some others opinions...because really i'm dying inside because of this. It just hurts me so bad to see him cry and know its bothering him and I feel like theres nothing I can do.