Can i get an std from sharing drinks with someone who had blood in their mouth or has given oral sex?

Nope, no worries: They call them "sexually transmitted" for a reason: they are passed from person to person only by sex. It's possible to have oral infection with some STDs, but oral STDs are not transmitted except by sex. Even open-mouth kissing doesn't transmit STDs. Oral-genital contact sometimes does so, but not all that often. For sure the is no risk from sharing drinks.

It is possible: It is advisable not to share drinks or food,