My boyfriend called me another girl's name during sex

We've been dating for a really long time, and I know he loves me. But today while we were having sex, he said another girl's name. She used to be his best friend, but she killed herself two years ago. I didn't actually even notice, he told me after we were done and I know he felt really bad about it. I know he was in love with her before she died, and he still loves her I think. I don't know what to feel though. I never had any doubts before, but now I'm wondering if maybe I'm not just a stand in for her.