You were just a kid. You were young and inexperienced. Some people, who are older, are in the habit of pretending that humans under 25 are fully functional adults, but those are delusional (or hypocrits who are just exploiting those kids). You were a kid, and your lack of experience weighted heavily on the balance. But experience is to be acquired for you to know what is what.

How could you have done otherwise? It was just consequences arising from a series conditions.

As for that "master", you shouldn't be fooled. He outted himself as having less wisdom than you (which is why you should go easier on yourself, by the way, you seem to be doing good with your intentions).

If you haven't done it already, take the Five Precepts and uphold virtue. Not only will they actively protect you, they will protect others from you by making you harmless (and therefore making you blameless). Keep them long enough, and you will easily be able to see the effect they have over time.

Be gentle.