Could really use some advice... 🥺🥺 threatening to take my son

So this is a long read, but please take the time to read it. I have been with my partner for nearly 7 years, and we just had our son together three months ago. We were both each other‘s first everything, and first love. Who used to be so perfect together, the healthiest relationship ever for about four years. Then out of nowhere we started fighting a lot and things got pretty toxic. He did some pretty shitty things, and really broke my trust, but we’ve been trying to work on things. Although I felt like he hasn’t been fully invested, which he even admits. He says he loves me but we fight too much, I try to express to him the reason why we fight is because he is emotionally abusive to me. He always tells me how I’m a dumb bitch, a cunt, any terrible name you can think of he calls me. He told me I was a lazy mother because I put our son down when he wasn’t fully asleep. Our son was drowsy and half asleep so I set him down a little early and he literally fell asleep instantly so I have no idea why he told me I was lazy for that. he also accuses me of stealing his money all the time, or stealing this or that of his, which I literally don’t do, and he ends up finding later. And I get really upset when he says these things to me and ask him why he’s so mean, and he says that we should separate because he just doesn’t know how to be nice to me.. That he loves me and wishes he could be with me, but just can’t because he can’t be nice to me. I do everything for this man, I’m the only one to cook, I’m the only one to clean, and I take care of our son a majority of the time. After he told me I was a lazy mom I got really upset and we got an argument, and that is when he left me (New Years eve) He had his mom come pick him up and he stayed at her house, he has done this multiple times in the past couple months since our son’s been born. Or he threatens to all the time “should I just leave & have my mom get me” . I begged him to come home the next day so he could at least help me with our son... he said he wouldn’t but I begged until he said OK. He staying with me until the seventh, which is his 24th birthday. Then moving in with his mom. He keeps telling me he wants to have our son in his primary custody, which I am NOT OK with. That’s my baby, and I am the sole provider for him now. I take care of our son day in and day out, he doesn’t.. I told him he can have our son Saturday Sunday and Monday. And I will have him Tuesday Wednesday Thursday Friday.. He yelled and said no because those are his only two days off, he won’t have a single day off. I said your son shouldn’t be a burden, he said will you get to have the weekend off and I don’t get to have any days.. I told him that’s just how things work with people and situations like this, if you ever want to have a weekend off for himself that we can always work something out. But it’s important for a child to have a stable home and routine... especially since he’ll be living with his mom for who knows how long, I don’t like the fact that it’s not a stable environment and my ex is literally living in their back room. Not even a bedroom, just like an extra living room. I hate this idea, and I also hate it because I feel like he will always have his mom babysit, while he does whatever. he tells me he’ll take me to court and get full custody since he makes a lot more money than me and so on and so on. I love this man so much, I’m so upset that he’s leaving me,  he’s literally breaking my heart, I feel like I’m losing it. On top of that, threatening to take my son and have full custody :( I couldn’t imagine going a week or so without my son.  I just need some advice on the situation, whether you’ve been through it, or anything to ease my mind because I feel like I’m breaking down. 

I should mention he has a good job and is about to buy a car then get his own place. Just no idea what his timeline is. We agreed he atleast pay his half or rent till the lease is up.