Is this a bad sign?

I'm dating a guy I met in high school and we recently just had our 3 years together. We used to hangout literally everyday when I lived at home and we had sex...a lot. We just moved into our first apartment, so we've been living together for 6 months. But I never really have the need to have sex like I used too and he constantly has the need. Even when I feel in the "mood" I never act on it because it never lasts long... Is this bad? Will it pass? does this mean I'm losing interest? Help!