This is my first time posting, I just needed a space to vent. Please don't be mean, I've been on Mumsnet recently (first and last time) and while most replies I got felt supportive the few that weren't really got to me. And yes I know- how niaeve to go online and expect everyone to be nice. But if I hear the line "but you knew he had kids before you got together though." I think I'll have a nervous breakdown. 

My story is a very long, very difficult and very complicated one which I don't want to get into until I feel more comfortable but really I'm here because I'm at the end of my tether and I'm just desperate to talk to someone who's been through/ going through something similar. 
A basic background- 5 years ago I met and fell completely head over heels for a lovely man (he is a good man let me just state this now.) - 17 years my senior. He had two boys to his ex-wife, at the time he didn't see them and was going through a horrific custody battle, which I was fully supportive of. Eventually he was back in touch with his youngest- J- (his oldest still doesn't see him). He saw him weekends and holidays. At the start things were fine between us all, even when a few years down the line I gave birth to our son J was ok with it. But at around my sons first birthday J decided he didn't want to see us anymore. From then on we've seen him sparatically- he's lived with us full time for weeks at a time, or at his mums and hasn't spoken to us at all. I do care about J- let's us get that clear at the start.He's had a complicated and difficult childhood and as a result he has many, many serious mental/emotional and behavioural issues. He is very immature although believes himself to be an adult (he's now 12) so doesn't respect me or his Dad. He is self-entitled, a liar ( who has made up vile things about me in the past), he is manipulative, controlling and has had violent outbursts. 
For the most part things are civil between J and I on a day to day basis. But truthfully I wish more than anything he was still with his mum- I'm resentful towards him and have never forgiven him for all he's put me and partner though. My family and friends try their best with him but they secretly can't bare it either knowing the things he's done to us. 
His mum- and here we go playing into the stereotype of a "new young wife", is not a good person, she is posionous. She has literally abandoned him several times, made up vicious and dangerous lies (one resulting in a police interview) about my partner and constantly puts her own gain and personal grudges above the well-being of her son. (My partner left her- but long before we met.) 

Hes now been living with us full time since Oct 2019, he has seen his mum a handful of times and she's made no effort to see him. He has no social skills and therefore no friends so literally spends every weekend with us. He expects us to entertain him every night, when after running around after two small children all day I'm exhausted and just want at least an hour with my partner to watch shit adult TV and talk about whatever the hell we want without child filters.
I've struggled, I've really bloody struggled with his presence, my feeling towards him, his self-entiltilemnet and his behaviour. I've been a teacher for 6 years now and I've never met a more difficult child. 
I've felt at my lowest, I don't know who I am anymore. I'm just so sad all the time. I've lost who I am and as a result I'm not the best mum I should be to my own kids who are missing out. 
 

And now, here we are, COVID19 is here and the UK is almost 2 weeks into lockdown. It's horrific and yes I know it should put things into perspective but all being in the house together is just magnifying things and I'm not coping. At least when he was at school I got a break. 

I love my partner- sometimes I think I've loved him too much for my own good. But I don't think I love him enough to put up with this ( I had these thoughts even before lockdown.) I think if I stay I'll be miserable for the rest of my life. 
 

And I really hope this place isn't like this but before I get a barrage of criticism- 

1. I know it's not and fault he is the way he is, he's a result of an insecure upbringing. 
2. Him living with us full time was NEVER on the cards. I can't even express enough how much this was never a remote possibility. 
3. I have sacrificed so much for my partner and for J. Normal experiences I should have had and yes I'm resentful. 
4. Yes I knew my partner had baggage when I met him but never the extent of what it's been like and honestly, sometimes I hate him for letting me get in so deep when I was so young and he knew how crazy his baggage was. 
5. I don't want to be a single mum. I don't want that for my kids. They didn't ask to be brought into this world but I did so with love, hope optimism and, I hate to say naivety. 

I don't know what to do. 
Sorry I just needed to vent.