So my dad has a new girlfriend, its been 4 months and she is already moved in..?

Wow, you've got some serious issues here. First, hide all of your important stuff and money, even if it means storing it at a friend's house. Your dad is obviously in love, or out of his mind, so reasoning with him won't likely help. Does your dad's mom or dad live nearby? Maybe you could have them talk some sense into him, or go live with them and tell your dad why. I can't help you with any ideas, but I can offer my sympathy.