First of all, it is totally fine to leave a woman if you are not attracted to her anymore. I myself had the experience of being with ugly women all my life, yet they got better each time.
The first one was morbidly obese with suicidal tendencies
The second one was very ugly facialwise but skinny and rather normal behaviourwise.
The third one was ugly facialwise, but skinny and well-toned with a character rather similar to mine.
I coming closer to my ideal, that is skinny, well-toned, with a beautiful face and great character.
No, you are neither an idi0t for wanting something better nor are you unsympathetic.
All those terms, "ass-h0le","you can get accustomed to it" come from a loser perspective, a weak mind that accepts low quality or a woman who wants to be accepted because she exists. Don't let anyone, especially not women, tell you that you have to settle for less.
Be warned, women will try to tell you that over and over. If women say, that they got accustomed to an averagely looking man, it is because women are rarely attracted by looks in men. Do not make the mistake of talking yourself into being a failure because of what you want. You are, because you are male, and they are not, because they are female.
Again, do not take advice from women about dating. Ever.
You, my friend, are coming from completely natural male biology.