How do you respond/react to "I love you" when the feeling is not mutual?

I've been saying "Thank You" for now, not sure how much longer that is going to fly. She is 19 years younger than me, I am not sure if it is age, I just know I do not share the same feelings. When we go out she orders a lot of shots and then the I love you's start flying. I am trying to help her not drink as much, getting her to drink some water before doing her 3rd shot but she is stubborn. She does not drink that much otherwise, only when we seem to go out.
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Adding a little more context from one of my replies:
She's always drunk when she says it. I don't see a problem dating people with the end goal not being married, I have no interest in getting married or having kids. To add a little more clarity, she splits rent with her ex-boyfriend who no longer lives in the apartment. I told her to move out since he has been known to show up there causing her to couch surf, she wants nothing to do with him. Until she sorts that part of her life out, she won't be hearing those 3 little words from me.


Source.