I think it really depends on what stage he's in with the Marines. Is your guy fleet? I think your guy would be able to answer that question the best.

i think they can stay the night with you... but a good idea to have a cell phone...
but not if he has duty ..... i dont think

my then boyfriend ( now husband ) is a corpsman and he had medical duty once and thought that he wouldnt get called in over night and he drove to my house 2 hours away from base but gave the keys to another corpsmen who was allowed to hold the keys to the med station.. plus he got permission from his chief but was told that if he got called that he would have to come in.... well a marine punched a wall and broke his had ... and the other guy who was suppose to hold the keys wasnt answering his phone so my husband had to drive back to base at like 1 am to go check out this guys hand... only to tell him that he had a broken hand and needed to go to the hospital where they could give him a cast...

Depends on whether he is in training, etc. I would say call his company (if he is permanent party) and ask if he can come. If he is in training it solely depends on the schedule. You can call anyway and ask.

If he is in the fleet,yes. My husband does everytime I come up. He just has to leave around 4 to be at base on time in the morning, which sucks, especially if you have to drive him.