I have a 8 yr old and I am 7 months pregnant. I have only been married since April 2007. I found out that my husband has been cheating on me for over 2 yrs. Also he slept with the person on the day of our wedding before we said any vows. For the past 5 months or so he has been in and out of the house staying where ever, and just recently got baker acted for going crazy and now this past Tuesday packed a bag left, he left our son with our neighbor while I was at work, left his phone and took off. He did not leave any note or any way to contact him. I tried to call the person he left with at least 4 times and left messages and have received no response to my calls. What can I legally do. I would like to change my doors on my house, and help protect my son and myself as much as possible. I do not trust him with anything. He had already told me that if I changed the locks on the door he would break it down. I live in Florida don't have a whole lot of money but need to figure this thing out. ASAP

It is your home, while you can not "lock him out at this point" you can always change the locks with all intentions to give him a key "latter". Now if he breaks in, I doubt he is breaking any law at this point.

You need to file for custody of the child, and file for emergancy order of child support. ( not that he will most likely pay, but get it in writing)
Most likely you can not actually file for divorce while you are still pregnant ( each state is different many you have to wait till child is born)

Sounds like divorce. Get a good lawyer, change your locks, go to court, get a restraining order, and did I already say it, change your locks. If he has ever physically abused you, go talk to a magistrate (and a lawyer) right away.