I am not an alcoholic, but I am in a Twelve Step program for another issue. I am an addict. Alcoholism, and other addictions, can be considered a two-part disease.
There is a physical abnormality, which means that once the person consumes the relevant substance or engages in the behaviour, it sets up an intense craving which is extremely difficult to ignore. They tend to keep on drinking/consuming, feel compelled to do so, and will lie and cheat to get what they want. The need for their substance eclipses everything else.
Then there is the mental obsession, which persists even if the person gets sober. The booze (or whatever) is their default mechanism for handling life. Positive emotions or negative ones, boredom, sadness, joy, whatever - the little voice will be there telling them how good it would be to have some…. And they will promise themselves that it will be just one, and they will mean it. They will believe that, this time, they can drink in moderation. But then they have some, and the craving is back.
A true addict needs two things: abstinence from their substance/behaviour, and a way to deal with the mental obsession. It is possible to get out from under, but it is extremely difficult.
It is difficult to stop, even with support. But if he doesn’t want to stop, it’s a non-starter. Nothing you can do or say will make him stop. Only he can decide, and even if he does, he needs help to do it.
Assume he will continue to drink, and the lying and passive aggression will only get worse. Make your decision on the basis that that’s how it will be.
If you do go ahead with the pregnancy as a solo parent, get legal advice about access for him. Maybe if you make the court aware of his drinking and your concern about the safety of the child when in his care, they would make an order for supervised access only.