Deppression and confusion. Lose her!

Actually i am in a relation for last 4 years!!!recently the relation is not going well!!!i mean there are faults from my side because of which my gf hates me nowadays!!during fights i scratch her hands sometimes she also does the same!!sometimes we just say whatever we feel like and go to any height!!!and my one habit which is the sole reason fr the complications...i blackmail her that if she leaves i will suicide! Because of which she hates me!!and one more thing i tend to talk with other girls on facebook!!it seems a bit entertaining but she thinks i am cheating on her!!but i want to stop these things!!!whenever i think that i'll stop texting them!!it again happens after 2-3days!!!please say some cure!!i don't wanna lose her!!