My heart truly goes out to you HunkyDory.
I was brought up from age 11 by my mum and Stepdad whom I love as my real dad (who has been out of the picture a long time).
However things havvent always been so great. My younger sister was quite aggressive towards my Stepdad from about age 11 to around 15. She used to have really bad outbursts coupled with problems at school and with the rest of the family. He tried and tried to resolve matters.
Both my parents went to counselling with her, we had family counselling, SS were involved. It was a very difficult time until it all accumulated in my sister one day beating our youngest sister up and attempting to strangle my mum. My Dad had to physically remove her from the house and would not let her back in. Cue massive arguements between my mum and dad and the big divide in the house with mum and us kids on one side and dad on the other.
Ultimately SS came to the rescue and offered to take my sister for what they called "respite weekends" where they go off and learn agner management etc. And the whole family went back into counselling.
This was 9 years ago and although it has been hard the whole family is thankful that rather than chucking in the towel we persevered. My Parents who were ready to divorce 9 years ago are expecting a very unexpected bundle of joy in march and have never been happier than in the past 2 years.
And as for my sister. My stepdad will be walking her down the aisle in one months time as a proud dad. They get on better than ever and The whole family is just brilliant.
I am telling you this because at the time of all the trouble I was in the same boat as most of the posters here. I felt my mum should have just chosen my sister over her DH. However now I feel that if she had our broken family would never have recovered as it helped my sister (and the rest of us) face up to, and deal with a lot of issues. I would rather have tried and tried to resolve the problems and then failed than just given up.
To the OP, we obviously dont know the full extent of your situation but you need to get help for your son. If you leave with him what is to say his problems will not continue. Get the whole family some help from SS thats what they are there for, not just to take kids into care.
And Big Hugs to you 