I just ruined a man's marriage and life for a 5$ starbucks giftcard and I feel awful

For context I (27F) work at a Target in a mall. I usually take my breaks at the food court and chill with whoever is working with me.

This particular day I was eating with my coworker, let's call her Emma. Me and her are close and we like to shoot the shit. When she grabbed her food and came back to our table she said "look what I just found in my wallet!" and showed me a five dollar gift card to starbucks. Emma hates starbucks and said she was gonna throw it out, so I asked her if I could have it.

Instead, being a jokester as she is, she said "what do I get out of it?" I asked her what she wanted, and she pondered for a second, then pointed to a lady and said: "that's my old math teacher's wife. He was so bad" And then she took a napkin and started writing something then gave it to me. She told me to give it to her and not to read it or the deal was off. I considered for a moment then did it and walked back to my seat. I saw the woman read it and start crying.

"What the fuck did that say??" I asked. Emma snickered and told me it was a note saying that I was an ex-student of her husband and when I graduated he had an affair with me and another student. I told her it was fucked up, then forgot about it.

This morning, like a week or so later, I was watching the news and saw that this man get fired and divorced for "illicit conduct with former students." My stomach felt like a rock.

And then, I went to Starbucks to get my coffee. The gift card was declined because it only had 30 cents left on it.