One can tell if the departing person was toxic without a rush to judgment.
A while ago on the vwt iodine forum a made a post about how I observed that toxins exist in many realms of our lives, not just the physical we're accustomed to talking about: spiritual, mental, emotional, etc. In all realms I've found that there's a common process to removing them, namely that their exposure and dislodgement causes pain and irritation, and once they're finally removed, healing begins. Thinking about what I've observed about people in the past, the same holds true for toxic people.
So, when you dismiss a friend, if they leave with minimum fuss - maybe with some regret and sorrow but not additional problems - the problem was not with them, but with you.
If, however, that person tries to hold on, or gives a guilt trip, or seeks to inflict additional hardship or revenge in some way, that person is toxic, and the problem is with them. And you'll end up feeling a lot better, once the problems have finally subsided. By their fruits (and their problems) shall ye know them.