Male, was virgin. had vag sex. condom slipped off. inserted once after. only reciprocal oral sex after. std/hiv chance? supposed virgin girl but idk.

Yes a chance: Any sex whether oral or vaginal without a condom is a risk for sexually transmitted diseases (including HIV). The chance might be lower given only limited exposure however you can not be certain. You can not tell if a partner has an infection by just looking at them or not knowing in detail their sexual history. Get a check up with urine and blood tests to know your HIV status and STD status.

No way to know: You had genital contact with someone of unknown STD Status. Get tested.