Yes. In fact, some STDs make you more susceptible to contracting other STDs. That’s why it’s best to get tested for all STDs
Yes,
Getting treated for an STD does not mean that you are unable to contract the STD again.
Condoms increase your chances of preventing STDs, but they are not 100% effective in preventing any and all STDs.
Most STDs are curable, especially when they’re caught early. HIV and herpes are STDs which have no known cures but can be managed with antivirals.
Certain STDs can be transmitted through non-sexual contact as well as oral and anal sex.
(See: Are all STDs sexually Transmitted)
While all STDs can be transmitted through sex, some of them may be transmitted in other ways.
Many STDs may not show symptoms, or may disguise themselves as other illness/disease symptoms. The only way to be sure is to get tested.
Technically there is a difference between STDs and STIs. An STI (sexually transmitted infection) is an infection whereas an STD was an infection that developed into a disease.