Nothing wrong with protecting your family. The fact is, this guy is dishonest and unreliable, and has continued to be this way. I know it's painful, but you deserve better. Make appropriate legal arrangements. Since you were together for so long and have a child together, that may even constitute common law marriage. Don't let him jerk you around - take control of your life and your situation. Use what support network you have to keep things together as best you can while in this transition.
If there were any way a relationship between you guys would work, it would need to start with him doing a lot of work on himself, and earning your trust, or else history would be doomed to repeat itself. Don't tell him he needs to do this, let him figure it out. If he really cares about you, he'll do it on his own... but I wouldn't hold my breath.
I'm truly sorry for your difficult situation, but you must summon the strength to rise above, for the sake of your child and your own emotional health.
Best of luck.