Spit? Swallow? Or just stand back?!

[ClosetBi]

but don't we have like a small pore or something like that in the gum?

Nope. You have saliva glands in your mouth, but they only secrete saliva, they don't absorb anything. So long as you haven't bitten your cheek or tongue or something and you haven't cut your gums while brushing your teeth, you're absolutely safe. Spitting and swallowing both carry the same risk for HIV, and that risk depends completely on your dental habits.

What you SHOULD worry about are the non-lethal but still nasty STDs. You can mostly treat and get rid of these, but herpes is forever.