I cheated on my girlfriend but I want to get her back she is also preganant too? Need advice plz?

I'm sorry to say this but you showed your true colours by doing what you did. When couples fight, they often need some space, it's normal to want to talk about it to someone or be comforted, but if this includes any form of ual contact, then it's just plain wrong. You're also old enough to be aware of the possible consequences of drug and alcohol use, and to be aware that this is not an acceptable excuse, you are responsible for all your actions when drunk or stoned whether you like it or not. She may or may not forgive you, I don't know her so I don't know, but as far as I'm concerned there's nothing worse than when a couple argues and then one of them cheats straight away, I don't care if it's the man or the woman, have a sense of decency.