My bf was naked and i think he had precum on his penis before he dry humped and i think i was in underwear. can precum get thru underwear? and if i wasnt wearing underwear could i get prego if precum got outside the vagina?

Yes and yes : You are “at risk” ; do check your pregnancy test as soon as you can and if negative and if you do not want to get pregnant, ask a caring and knowledgeable clinician for a L.A.R.C. : Long-Acting-Reversible-Contraception with an IUD (intrauterine device) or a subdermal implant is the most effective way of avoiding “prego” ; use male and/ or female condoms too to protect yourself even more +better