Wear a Condom or pull out next time. With the abortion bit, I dont support it but its her choice. Be there for her, If you no longer have feelings for her, well dont leave her now is all i can say. If you leave her now it will be real hard on her.
During this phase look for portentous signs of depression. Remember that because you impregnated her she is your responsibility to look after. Ive heard of things like this causing in suicide, I know because its happened around my old neighborhood.