If space travel slows your time down in relation to people left behind, then why are you visible to them.?

If you aren't in the same time frame as they are, they should not be able to see you, but we can see returning astronouts. Is this where multiverses come into play?

No, no multiverses necessary. Just special relativity.

Just because your watch runs faster or slower than someone else's doesn't mean you can't watch one another.

this is just a shot in the dark, but astronauts would have to travel much farther than the moon for time to make a huge difference.

as for multiverses...that's some star trek type stuff, and i couldn't even has hazard a guess...i'm thinking that i have a goatee in at least one of these multiverses.

The other person would look weird.

It's not that you're in another dimension or parallel universe, it's just that time is slowing down for you (assuming you are the astronaut). Really, you'd need to be going much faster than astronauts typically travel to notice a big difference anyway.