I don't believe it makes you an arsehole. You don't owe anyone anything and you're only responsible for your own emotions. Don't let anyone walk into your life and command things you're not ready for.

The difference is that you're ignoring someone you have no connection to any more who has shown up and demanded attention without deserving it. When Harmony ignored you, the two of you were together and you'd made an agreement through that to be there for each other. She broke that agreement, not you.