I need advice about what to do about if you start heading for a relationship but then change your mind for some reason part way in, what should i do?

Ok, so this girl and i made out right before our winter break (we were actually interrupted by her having to head home that night, and my being slow on hints, but that’s besides the point). I really like this girl she’s very smart, knows what she wants to do with her life (at least for the most part), she is of course quite attractive. Here’s the problem though, and i feel like an ass hole, but i can’t really explain it. As we spent time talking after we resumed our making out from before break after we got back, no sex but just about everything in between, well she starts telling me about all these allergies she has, and how she has some sort of genetic skin condition where she gets dark scars from her alergic outbreaks (like an exhima but with bad scaring). We had a great time but in the back of my head i’m thinking that i am not interested in the relationship continuing, and the only reason that i can think of that is making me feel this way is, i feel, her genetics. she’s a great person, and i feel like an a** hole for even thinking about this. Am i really as big an a** hole as i feel?