I took my daughter to a museum when they had a special exhibit of Marvel Comics history. She very excitedly (and thoroughly) told me all about each character. Was I as enthused? No. But I learned about her interests and we had a great time together. She’ll always remember that.

That sounds like it is not a mistake. I am fairly sure that he has listened to you about your passions (hobbies/gossip/work) that normally do not interest him. What did you learn? You learned that he enjoies gaming. You learned he enjoies the historical integration of the Assassins Creed series. You learned he likes the intrigue introduced. You learned that when he is not gaming he is with you. You learned that when he is not with you he will want to be gaming. That means he is not cheating on you. That does not sound like a bad thing. You have cemented his feelings for YOU by listening. You know, just like when you describe your life to him. Take the win.

Never engage a geek on their specialist chosen subject unless you want the full TED talk. However, said geek will absolutely love the opportunity to geek out and one of the points of a relationship is giving the other person what makes them happy. You made him happy, it was a chore for you but now he loves you more. That's the win. Buy him an AC t-shirt or something cute and watch him love you even more.

What a loser. Let me tell you about The Legend of Zelda, a game franchise so good Robin Williams named his daughter Zelda. And if you think Assassin's Creed's lore takes hours to explain you're gonna want to sit down and drink a ton of coffee for this one.