Why do i get so angry when my girlfriend dosent want to have sex ?

Work on yourself...: Sounds like you have some limiting beliefs that are triggered (causing anger). You NEED to know that this is YOUR issue to work on! Your girlfriend has every right to make her own decision about sex and her body. She doesn't deserve your anger. Work on relaxing, meditation&figuring out what "stories" you tell yourself that lead to her decision feeling like a personal rejection (it's not about you)

Hard to say.: It depends on the circumstances. If your relationship makes you angry frequently, you both need to talk to somebody. Sex (giving or receiving, or the withholding of it) can be a psychological weapon. Open communication, without anger, is a good way to start. This may not work and then working with a professional can help you have a happy relationship and a healthy sex life.