Being a JW is his choice, he is trying to force you to make it your choice too. JWs with his mindset do not compromise and are not interested in an alternative point of view. His infidelity may make him feel that he has to work even harder to be in an approved state but if he hasn't confessed his sin to the elders he will know he cannot earn God's blessing under JW rules. The problem is he is making you do his pennance with him which is unfair and unreasonable.
If his behaviour is having a negative affect on you and your child then it may be time to change things. If he is not interested in what you want then separating from him and giving him an opportunity to realise that you are serious may be necessary.
It is incredibly difficult dealing with lapsed JWs who still believe because you are never free of the religion it is a shadow hanging over you. In such a relationship there is a danger you become marginalised and seen as a problem that will make it harder for him to progress in the organisation. He needs to decide what is important to him. You need to look after your child's interests sine he is being selfish and focusing on himself at the moment.
I wish it could be more positive, I really feel for you.