Posting more details would be really nice, cause if that last bit was sarcastic then lol nice, and hope your relationship goes well, if not see my prior comment.

Too bad there isn't an: "I wish I could punch you in the face" button. I'd click that one. Your poor girlfriend. Fhl.

So tell your girlfriend that, like a responsible adult

Looks like you need to man up and tell her that you have no intention of ever marrying her. It is clear that the two of you have not had that conversation.

This post would have been just find ending in "but I wasn't planning on marrying her".

Why have a girlfriend if you don't want to get married?? You're tied to her without a ring simply by being in a relationship with her.

Uh, yeah, wish I could talk to the gf, she needs to move on. :)

Have a nice lonely death

If you're so strongly opposed to marriage why doesn't your girlfriend know that? It's a pretty reasonable and common expectation for a committed, long-term relationship to eventually lead to marriage, so if you feel differently you need to be up front about it instead of assuming she'll just know somehow. The only thing "sick and immoral" here is if you continue the relationship under false pretenses.

F YOUR life? Dude, I feel more sorry for her to be honest.