OP - you've had amazing advice on this thread. It's not surprising that you don't know whether you're coming or going.
You were clearly vulnerable at the outset of the relationship - any sensible woman would run a mile from a drug-addicted ex-con, no matter how physically attractive he was; even more so any sensible woman who had children.
You are even more vulnerable now that you have spent some time being emotionally, mentally and physically abused by this man. Make no mistake - he will probably kill you if you don't get away. He has already tried to do so twice (that's what strangulation is). As previous posters have said - strangulation is a strong indicator for future serious harm and murder - and this man is repeatedly looking for excuses to be angry with you so that he can justify further emotional, mental and psychological violence. He is incredibly dangerous to you and women and children generally. He sounds capable of killing your son, too, so it's just as well you've lost custody of your son for now.
The difficulty is that the intense highs and lows which come from abusive relationships can in some ways become addictive. Even abusers are capable of behaving well and the good times can feel even more ecstatic in an abusive relationship because of the relief, the contrast with the bad times and also because abusers can love bomb like there's no tomorrow. Women Who Love Too Much by Robin Norwood explains this very well. I think you are addicted to this relationship and would find Robin Norwood's book helpful.
It's clear you need external help to extricate yourself from this relationship.
Right now - do you have a family member or friend who could move in with you for the next few weeks or someone you could move in with? If necessary, could you manufacture a story that a family member/friend is visiting and/or ill and/or needs somewhere to stay temporarily? They could then move in with you or you could go to them and buy yourself some time away from this man.
You can also start speaking to Women's Aid for advice and also speak to the police and explain your situation.
Remember - if he goes back to prison for his actions, that's down to him not you. But also - he will have to go back to prison for a lot longer if he kills you. So in fact by reporting him to the police now, you are protecting him from the worst excesses of what he might do, as well as protecting others from him. He won't see it that way but it is the truth. You're not helping this man by protecting him from the consequences of his violence - you're actually harming him and doing so at immense personal risk and cost to yourself and your son.