Custody Rights During Arrest

In August of *, my sons father filed for a motion to modify our custody agreement that had been in place since December *(we dated from Jul *- Nov *..(never married) my son was just a little over * at the time of the split). Since we have been split up, he still continues to try to control my everyday life, threatens me, keeps my son from me, harasses me, stalks me. We had an ongoing custody dispute that ended in May *. He could afford an attorney, I couldn’t, and was also denied legal aide numerous times.he ended up with full legal and soul custody of our now *. Y/o. I’ll attach a copy of “modified agreement”. He does not follow it whatsoever, and still keeps my son from me. I’ve maybe see him 2 days a month if I’m lucky. 
Through the course of our court battle, i finally became brave enough to stand up to him, and actually go to the police and file charges on him January * for stalking and harassment. I filed sexual assault charges on him in august of *(in order to see my son I would have to do things I wasn’t comfortable doing). If I said no, he wouldn’t let me see him it talk to him at all. This has been a long process of waiting for the charges to become anything, and i have had a detective on my case since the charges in august. My detective just informed me that he now has a warrant for first degreee harassment (felony class E) I believe (may be mistaken). My question now is, what does this mean for my son. Since there is a warrant, he will eventually get arrested.. I expect him to probably have a bond, and he will make it no problem no matter how much money. Do I have the right to go pick up my son if I’m informed of the arrest, and am able to before he’s bonded if he iis with his girlfriend, or mother, or sister? Say he doesn’t get bond, do I have the right as his mother even though he’s the custodial parent, to locate my child, and take him home? If so, of course I plan to file for emergency temporary custody, and take him to court and request full legal and soul custody of my son. I would now if I could afford it, but I am starting a job next week and plan to use everything cent I earn to find an attorney that will help me and take payment plans and put everything down for a retainer. 
 there’s so much I could add about this case and things that happened (but I tried to stay on point about my main question at hand throughout court with the Gal, abuse, Insane voicemails I recieved from him when my son was present with him and heard it all. It’s honestly so sickening. He mentally and emotionally causes trauma to my baby daily, he has said things to him like “you’re mom doesn’t love you” “she’s too worried about being a whore to be your Mom”. My heart is completely shattered that I’ve been unable to stop this and get my son away from that emotional and mental abuse.

Thank you

Misssouri