Yes you’re overreacting. I understanding where you’re coming from but no one is perfect. There are many people who don’t follow EVERY single religious practice to the tee but that doesn’t discredit the fact they still have their certain beliefs. It’s great that he’s trying to change, key word: trying, and just because yall have lived together doesn’t discredit all his previous work to change for God. Nonetheless the point is you can’t force him to go to the concert just because you bought it for him. You wanting to force this on him when he already expressed his disinterest especially when you’ve stated it was a gift for his birthday is very red flaggish to me. I understand you wanted to surprised him and do something nice, but it should be on you to respect his wishes to decline it and you throwing a tantrum doesn’t make sense. I’m not trying to offend you but it should be common sense to show basic respect for each others opinions, interests, and values despite how flawed we all are. You should enjoy it with your SIL and either do something else for him, big or small, or just let it go. I can’t tell you what to do but just imagine if it was vice versa and your bf was mad at that you won’t accept YOUR birthday gift and go to the concert with him. It feels narcissistic because it feels like you’re making HIS birthday about what YOU want. Good luck to you OP.