Them knowing doesn't actually matter as long as an outsider looking in has no proof beyond their word. It becomes their word against yours, so you can say they're lying because they have an issue.
It's a good lesson in being careful about what you share. You can't undo that this person knows about the comic, but if they've never done anything to hurt you before, there's no reason to assume they will in the future. I do think you should be careful, but I don't think you should make a significant change to your life when there's no indication this person would actually cause you any harm. You can only worry so much about a hypothetical situation, right?
Edit: Editing just to add that you shouldn't feel bad for sharing a part of yourself with other people and being betrayed. Thats on those people for hurting you. Trust is a wonderful thing, and it's natural to want to share something you're excited about with others. You're not bad or wrong for that. It's just a sad necessity that we have to be careful about what we share.