Please as I said seek some impartial , supportive, non judgmental advice from a professional source regardless of your decision to stay with him or not.
Many women are triggered who have very sadly like myself been through what you have, accordingly feelings run high for women responding to your posts. They can see the future and consequences whereby you are so emotionally invested and now tormented , expecting twins, so as you calm down react defensively too.
They don't meant to be mean but one of the questions you answered in another of your posts is that it is your house.
So many women fall foul of the sad guy who has split from the previous relationship for cheating, telling the tale that they have never felt like/ loved as much the woman they then rapidly move on moving into ready made , loving homes, that they couldn't afford themselves ...whilst the previous partner and child are left to cope with the fallout and she assumes full responsibility for the very young child/children , as you did previously yourself.
I wonder if his tears are for the fact that he could lose all the comfort of a loyal partner and home set up. After incidents like that men don't cry, they also pick up the phone even when out of it if they have nothing to hide and do not make up fake stories afterward.
It is also not the first time he's done this , only the first time to you ...
If there was sensibility in the situation there is no way someone who has been up all night taking cocaine and drinking heavily, hanging would risk driving and putting a small child in the car. No excuse in this day and age.
You posted the child's mother knew what he had done yet still let him pick up her son, you are also his step mother ( please do not think I am suggesting his actions are your responsibility). However all children should be treated as equal in my opinion in blended families.
How awful for the children of people that go from one family to another, nobody questions the effect on them which stays with them and they out of everyone are the most important people.
Sadly these days many people move on with speed starting new families without much thought to the fact that most second/ third relationships do not last the course , it has become the norm just to move in and out, particularly men when the going gets tough and they already have children from previous relationships. With all the will in the world for the happiest outcome, for which you may be an anomaly and he may prove those that are interested in your best outcome wrong .
Please I urge you be wise, seek kind, professional support , protect what you have and your children, you are between a rock and a hard place and if I were you come off Mumsnet for a while , learn to trust your instincts and be kind to yourself , nobody can think straight in the early stages of pregnancy when feeling sick and exhausted all the time. This kind of situation is not good for unborn developing fetus's either.
Give yourself time and space, x