Apologies in advance for a long thread - everything is such a mess but I don't want to drip feed. I think my marriage is over, and I'm devastated.
Been with DH for eight years, married since 2011. We have a 2yo DC. We broke up briefly last year and I moved out with DC, but I moved back in and we've been trying to make things work.
The negatives
Things have always been a bit volatile between DH and me - we're both hot-tempered so lots of arguments. Verbal abuse from both sides, more from his initially but things devolved over the years; emotional abuse from his side, including horrendous threats when I'd just had the baby (having it taken off me, using his ££ to win custody and have me declared an unfit mother), calling me a dirty cunt etc.
We're from different cultures - I don't like his mum, whom we see every week, at all and there's a risk she'd end up living with us / expecting to live with us later in life. His younger (by one year) brother also has very mild learning difficulties (I suspect undiagnosed ASD also) and lives at home/doesn't work/doesn't leave the house. Again, I suspect later in life, he would want to come and live with us.
Mismatched sex drives - mine's always been higher, he's literally never (in eight years) brought me to climax 
and now it's at the point where we've not slept together since I was pregnant. He tries to be affectionate, and I want to want him, but I don't. I get that things can't improve if I won't have him near me, but...I don't know. We have separate bedrooms; I go to bed around 10pm (up around 6.30), he goes 4am (up around 12.30), although I get a lie-in on weekends.
I cheated on him last year. It's not an excuse, but I was massively ill with PND and I was targeted by someone who I thought was a friend. Turns out they weren't and I was being manipulated while vulnerable. It's the only time I've ever cheated on someone, but I know it's a shitty thing to have done.
I've recently got closer to someone I know from work. It's at imminent risk of turning into an emotional affair, although we've put the brakes on it because it's (see above) a shitty thing to do. It's really upset me, though - I'm lonely, and it's ridiculously hard to not want this colleague.
We don't share friends, interests or schedules - the whole permanent night shift thing means we can never have a day trip anywhere, for example, and I find that really hard.
The positives
DH and I have taken care of one another and been together a long time.
Over the last year, arguments have decreased - he's been working on his temper, as have I, and we do argue less.
He wants to work on things now and try spending more time together. With the now 2yo, family problems on my side etc., we've had less than a year since my brief move-out to try and sort things out. He's apologised for the shit he's pulled in the past (emotional abuse primarily) and outlined ways he wants to improve, and has improved.
He's honest and loyal, faithful and (outside of arguments, which are much less awful than in the past) respectful to me. He's doing more 'little things' for me lately and trying to be more thoughtful, communicative and considerate.
He pulls his weight in the house usually, and is relatively hands-on with DC.
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In a nutshell, I don't want this to be it but I'm not sure what to do. I don't want to destroy my DC's life and family. I'm terrified of not just being alone, but moving on from DH. But at the same time, we're more like friends now and I'm desperately lonely and upset.
Is it possible to come back from something like this? Is it possible to make a marriage like this work? And if leaving is the right decision, why am I so completely devastated? Despite our problems, he does care and I think he's a good person.
So sorry for the giant post - I'd appreciate any insight. Please be gentle.