Can I suggest putting this disclaimer at the start of the chapter where this stuff starts occurring? From what you've said I don't think it's going to be extreme enough to warrant a trigger warning but if you're worried you might hurt readers, then it's best to put a little note in the comic itself.
Very few people comparatively read the forums, and then even fewer than that are going to find your topic, so you're not really warning anyone. Personally i'd advise hinting at these themes in your blurb, that way if people are unlikely to enjoy that element of your story they don't get invested then frustrated it's going in a direction they don't like, PLUS as you've seen this is some people's jam and if you don't say that this stuff is in the story in the blurb people who love it are going to miss out.
