What do I do about my boyfriend telling me about his inappropriate student relationship with a former teacher?

My boyfriend (high school sweetheart) admitted to at least kissing on a former teacher. I was a late night cocktail discussion at his mother's house. She pulls the glass away from his saying "o. k. darling, you've had enough."
Indeed had enough to admit (after his mother left) to a make out session with his former Senior English teacher. The vibes the woman gave in the hallway made eerie sense now. I don't know if this was the extent of it or if I "shared him shared him". Any thoughts.
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I gave him some more happy juice to talk last night. They had their tryst close to the day we first spoke. That's what I could get out of him. And let me say he get's snooty when drinking. Telling me he could have any female who is supposed to automatically fall for him because of his personal appearance. It hurts. Other girls crushed on him (some DO NOT like him) but I was the one there for him.
What do I do about my boyfriend telling me about his inappropriate student relationship with a former teacher?
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