Hi A.,
You are right. It sounds like your son has gone through a lot and it is affecting him deeply. If, as you say, these are new behaviors, he may be having a lot of feelings about babies and how they affect his life. I have a few very brief suggestions / questions:
RE his dad: Does your son get to see him, and regularly? This is very important to a little guy. If not, do what you can so that his dad knows how essential he is to his son and finds a way to carve out separate time for your son that is special to them, as well as some time with dad's newer family.
"Attitude": Suggest that you see his negative behaviors as having reasons behind them that make sense, and GET HIM SOME HELP. Find a good child social worker / counselor. He could do some play therapy and find an outlet for all of his feelings and slowly sort them out. Maybe some family counseling is in order. If you have a new baby in the house, include him, but realize that he will have reactions to losing some of your attention. This is normal. If you don't / can't do counseling, do some play therapy yourself with little dolls, including a baby, and the two of you talk about having a baby (through the dolls), seeing or missing daddy, etc.
Try not to react to his behavior (don't know if you do). Sometimes we get mad as parents when our child misbehaves instead of staying calm and non-reactive. Kids need us to love them no matter how they act.
Books: I like books by Louis Bates Ames simply titled YOUR ONE YEAR OLD, YOUR TWO YEAR OLD, etc. Get "YOUR FIVE YEAR OLD" and see what may be normal five year old developmental behaviors vs. real problems. These books are easy to read and not too long.
I am sure you'll get lots of suggestions. Good luck with this and with the new baby.
Barbara