NauticaMen's 3-pack Classic Underwear Cotton Stretch Boxer Brief Boxer Briefs (pack of 3)

We hy don't they have a fly?

what does "pull on Closure " mean?

I have a 32 waist, should I get a medium or large ?

Do the the bottom part of the briefs get loose at the end of the day? Do they stretch out and stay that way?