In some cultures, this is the norm; I wonder if they suffer such anguish as we do in cultures where monogamy is the norm? The thing I liked most about this piece is that it’s easy to imagine being any one of the three characters in it, and to feel that shared anguish.
As for the nasty comments you got (and the ones Heather Nann got) they’re inexcusable. Readers should be mature enough to recognise that maybe, if they don’t like your writing, they should be reading someone else’s writing instead. At the very least, they should speak with respect for you as a person, and simply address the points you’ve made and their disagreement. If your writing upsets them, they can state why without resorting to name-calling. It’s not kindergarten.
I don’t think you should need to take action to avoid comments like the ones you received, any more than you should have to dress a certain way to avoid being harassed. Further, deliberate ambiguity can be a powerful literary device, stirring up strong emotions in your readers, so you should use it whenever you damn well like.
But if you do want to avoid ambiguity in future, you can always tag your writing with the topic ‘Fiction’.
A better reason for adding that tag is so that all the readers out there who love fiction, and especially those who are following the topic, will be able to more readily find your writing and appreciate it.