This is not something YOU can fix. This is something only he can fix. But from what you describe, it doesn’t sound like he even acknowledges there is anything that needs fixing.
You say you know he has it in him to change. Based on what?
For your sake and for the sake of your child, I hope you can accept that he is not the person you want him to be, and there is no guarantee he ever will be. Now is not the time to rely on hope that he will improve.
You do deserve a partner you can trust and your child does deserve a loving father. He is not that man right now.