Can I be fired for something I said to a coworker outside work?

A disgruntled ex-coworker sent a screenshot of a mean text I sent to them about my boss. I’ve only ever been polite and respectful to my boss. The text I sent was supposed to be private and the ex-coworker sent it to my boss without my knowledge or permission. My boss fired me immediately without conversation about it. There was context to that situation for sure but…thoughts?