Sleepovers

I'm 23 and engaged & live with my fiancé and dog. One of my coworkers and I are really close (she's a girl) and we've been talking about having a sleepover for a while - I live 3 minutes from our work. I told my fiancé she was going to spend the night this week & he made me feel bad and asked me if I'm 12... Then I asked my mom if it was weird to have sleepovers and she had some negative sarcastic comments for me as well... Is it really that weird?