Having second thoughts about proposing to this girl... Help?

With ALL the likes & dislikes between the two of you, I would definitely say the two of you would NOT get along well together whatsoever. I would NOT consider marrying her as there's NO doubt in my mind the two of you would NOT be happy together. Just tell her you don't feel you two are the rite ones for one another & both of you go your own ways. Don't keep her on "the hook" for any length of time, let her know as soon as you can it's just not going to work out, she goes her way, you go your way...good luck to you...:)