We want to get married but he has lifetime disability and 3 children by another woman they separated we engaged but she told me since he can't pay child support that if we marry she taken my income and I'm pregnant working part time since 2006 and we been together 3 years

If this is in the US, she is lying to try to keep you away from him. She can not take your money for his child support

... they seperated we engaged ...

Separated suggests that they are still married but living apart. You cannot marry him until he is divorced.