right listen now,
YOU ARE NOT A BAD MOTHER - YOU'RE NOT, YOU'RE NOT, YOU'RE NOT!
gonna stamp me feet more if needed you're not! lol. seriously thou, a questionable mother would be one who stayed after what he did, a bad mother would be one who left herself and left her children behind. you are so far removed from a bad mother. You're brave, you've put your son above all else. for the next few months you will have wobbles, you will have days of exhaustion when it's all you can go to get dressed (hell I still get them a year down the line) BUT know this - you'll be free, you'll have your own space, you can raise your DS in an environment where love and security play a key role, and violence terror & bullying is not allowed.
you know a lot of the lone parents didn't set out/choose to be such on the LP boards but we're all there for each other - and i'm positive if you have a wobble one of us will be there to help you pick up emotionally. I know you are scared sweetie, honestly it's very daunting and scary to step out into the world and worry now that every little desision you make is going to be the right one for your DC - even down to where you live & send him to nursery etc. the pressure does get too much sometimes. but with a good support network YOU CAN DO THIS. you can, believe in your own strength.
re his family - tbh what I would do is ignore them, log everything and keep your head high. I've come to the conclusion - and I prey I'm never like this with DS's future partners, that our MIL's kids are the apple of their eyes and can do no wrong. you will always be the bad guy, and you'll always be the one who took their son & grandson away from her - but you know what - all this aside you have the BEST thing of all, because you have your son. he is the best thing to come from this.
it is hard, but it's so rewarding as well.
(oh and as a final thought - right now in this moment, trust your family only, if your MIL comes across sweetness & light etc have an air of caution. when my X said he wanted out, my MIL sent a message to me saying i'll talk to him I had no idea etc etc laying it on thick, then I found out about a week later had sent one to XH saying 'don't worry son, I did it to your dad you can still have your son' )
tbh thou looking at your DS - you'll find the strength you need to fight this, it just happens, but please make sure you have family with you so if you do break down they can help you rebuild, & to a degree protect your & DS from a lot of things.