Drugs and Financial Problems during pregnancy?

My girlfriend is pregnant and she is always complaining about spending our money on marijuana, but she is 6 months pregnant and is worried about me being irresponsible with our money when the kid comes but thats 3 more months to save money. My friend told me to just push her down the stairs but that is extreme, and i dont even know if i want to stay with her since she got fat and ugly... What do I do?