Need help dont know how to go Forward.

Im 27 M and live with my son 5M and my mother and listen 46f and 19F live with me to help me with my boy.

Over the last 2 years my Ex 25F has been getting progressively worse, to the point that my son ended up leaving with me on weekdays, and his mothers on the weekend although thats been on and off

For context, my Ex and I got together when we were young I was 17m she was 15f ( we are about 2yrs in age gap )

We meet at a fast food joint we both worked at, at the time after a few month of talking and getting to know eachother we decided to make it official.

At furst everything was great, we spend time together sometimes I went to pick her uo from work and take her home and even helped her when her Ex at the time started to follow her.

Fast forward 14 months im 18 and shes 16 and we ended up moving together as she got kicked out of home, when I heard this I rushed to find any place so she wouldnt be on the street against my own parents wishes and ended up on bad terms with them for a few years.

At this point and I know this should have been a red flag but I was wearing rose coloured glasses at the time, she had told she cheated on her Ex with another man but that he didnt know and she promised it wouldnt happen again.

The arrangement wasnt pretty but we made it work, I tried to pick up extra shifts, by this time I dropped out of my last year of school ( year 12) and was helping her by covering her school fees and paying for the house.

Fast forward another year and we were making it work i was now 19, she was 17 and in her last year of school.

Until the other man who she has cheated on with came up, he started showing up randomly, when inwas at work mainly and she started being distant and denying me affection ( at the time I didnt know this bloke was the same one )

Things progressed and we eneded up breaking up, only then did she admit she had cheated, about a few months later we ended back together again, yes I know im stupid for it, and much to my surpise she cheated again.

I wont make excuses I did take her back again but I couldn't trust her as easely and I started becoming paranoid ( im aware I did it to myself and I have learned my lesson since then )

Fast forward 2 years and after going steady for that long after the 2 incidents she ended getting pregnant with my son, 21 for me and 19 for her ( what I wasn't aware at the time and would later find out was that she was cheating the entire time, which I guess I deserved for being soft and stupid and later I would find out after we separated when the kid was 6 months and she took him to live with her full time, that she only kept him because she thought it was the other mans, I havent done a paternity test as im scared still to find put the result, but I have raised this child for 5 years and if I eventually take one nothing will chnage )

I will admit during the 6 months after the baby was born things got worse, she started going out more, drinking and started smoking pot. ( which she was smoking during pregnancy but not as much since we fought about it constantly )

I will admit i messed up aswell , there was one time when were fooling around and I saw a bite mark near her thighs and I bit hard before I could stop myself and another when she had gotten a Hickey on bruise or whatever it was on her shoulder and before I could stop myself I poke it with more force then needed, I regret those moment and I have gotten help to get my anger under control now, and im doing much better, my therapist made me realise that I lashing out a lot of pent uo frustration anger and fear of everything in the relationship, but thats no excuse.

After we separated she started seeing other man and moving from house to house after ether a year or a few months, I know I should have acted then, but she always threatened me to call the police on me and report thise 2 times as domestic abuse and I was scared.

Then come 2 years ago me 25 and her 23, she got beaten by one of her partners, which I wouldnt wish on anyone not even her, so my son came to live with me as she didnt have anything steady, till this day shes still claiming centerlink and getting paid as if she had my son.

She has had many incidents during this last 2 years including drugs, being involved in that sprt of bussiness and not having a steady home or income until this last year to support our son even then she still wouldnt be able to afford it without the centerlink

Now at present she had an incident last nigjt she called and like an idiot since I still got a soft spot for her I dont know why I went to pick her up, helped her get a few things from her now former home, which she was reciding in, and found out she and her sister got in a punch put and she got kicked out, when I went in to get a few of her things thw sister 21F told she that my Ex 25F is currently doing Meth and Pot and thats why shes like she is.

At the same time on the drive last night she admitted she wanted me back, which I told her no as im doing better on my own cureently, I tried to be polite about it

Then this morning she texted me saying she was meant to go to to a different City to live with her Aunt and that she stayed for our son, but now she wants to take him and she thinks she can give him a better life when I pay for his schooling, aftershock care, food 5 days a week clubs, insurance and doctor visits ( specialist )

And as of recent a therapist for my son as his not coping well recently cause he wants his mother and I back together.

When I refused giving her permissions to take our son, she started the guilt trips, saying his not doing good emotionally which im aware sense the private therapist, and saying that im not doing was best for my son as he wants us together but I dont.

I have since yesterday told her mother ( as she had no phone at the time ) to tell her not to call me for things like this anymore and that im gonna put my well being first and dont want be involved in that sprt of staff anymore, shes welcome to call to check on her son but no more calling me for help.

As of now im currently stuck on what to do, as I dont want end up on bad terms but I know it might be unavoidable, do I file for legal sole custody, do I try to talk to her, please if anyone has any advice it wpuld be appreciated it .