Talk to him about the baby. Have him help you with the name. Let him interact with your belly. My son is 1 year and 9 months and he loves playing with my belly he will sing to his brother, and oddly enough named him berry and he loves to feel his little brother move. Little things to get him used to someone he can be friends with. My son is a big mommas boy so I know the feeling.
Yea my son is a mommas boy bad. So I can imagine how he is going to act when the baby gets here in Oct.
Try to do everything with him why you can take him out play with him a lot but at the same time let him know there is a baby in your tummy . I'm in the same boat but my son will be 2 in 2mo and its hard cause he want everything his way now he do a lot of crying for no reason and wanna be under me 24/7 I can't do nothing with out him been right there