How do you move on?

When you know the relationship isn't working or good anymore... How do you move on? There are times I decide it's bad and it's not getting better. But I can't follow through with moving forward without him. I don't think things will change but after an awful argument when he starts calling me or asking me to come over, I always give in. When I try to stand my ground he makes me feel selfish or like I don't really care if I try to stay away. I've repeated this cycle countless times. How do I stop myself?