Fantasizing during sex?

After my (28F) boyfriend (29M) and I had sex today he told me that while I was giving him oral sex he was imagining I was his school teacher and he found it really hot. I responded casually and supportive but for some reason it didn’t feel great to hear that. He has no idea I feel any way about it because I responded positively. I’m trying to process my feelings and don’t know if I’m being unreasonable. I’m fine with role playing if we’re both kind of in on it, but him wanting/needing to imagine I was anything else but what I was in that moment in order to get off makes me feel weird? Like I wasn’t sexy enough as “me” so he needed to imagine a scenario where I was working else. I don’t know. It might be silly. Or maybe I’m wildly insecure. I guess during sex I get off because of HIM. If I got to the point where I was imagining he was my neighbor in order to get off, it might signal to me I’m bored or not as interested in just sleeping with him that I need to imagine he’s someone else.

I need other peoples thoughts because there’s a good chance I’m overthinking this.