Am I wrong to be upset?

My husband friended his ex on Facebook and didn’t tell me. When I found out I mentioned it to him and he said “I didn’t think I had to tell you.” And I was like well yeah it’s an ex I thought you would’ve told me. You tell me about your random coworkers. Then he goes oh so you want me to delete my Facebook. Um okay?

It’s been 10 years since they broke up, why now? He hasn’t seen her since then and we don’t even live in the same town. I see no reason for it. They weren’t even together that long from my understanding and ended because she cheated. We used to have a joint account for about 6 years and never once requested her but now has his own account so all of a sudden. It’s just weird as hell to me. He got upset that I mentioned it. He’s the only guy I’ve been with and I told him how would he like it if out of nowhere I had friended an ex and didn’t tell him and he was like I guess I wouldn’t know would I. Got all defensive and said he can friend who he wants.