I need advice...

My fiancee is in the Navy and was stationed on the opposite side of the country. He leaves pretty often for training so we don't get to talk very much. We've been talking about me moving out there to be with him so that we'll have the chance to see each other when they're in port.

So my questions are:

1. When should I tell my Mom and how? I'm leaving around the end of December and he and I will be driving out there.

2. How do I settle her mind that we aren't doing this so we can have sex and that I'll have friends?

3. Is this an absolutely stupid idea?

TIA