welcome to HealthcareMagic
tobacco and even pot has been associated and has been identified as a reason for reduction in sperm count
but it does not make a male sterile.So even if your boyfriend has been smoking pot since 10 yrs he will not be sterile and so the risk of getting pregnant after unprotected sex will always be there.So hence forth if you don't want a baby then use protection or contraception
and for the unprotected sex you had last night you can take a emergency contraceptive
which a doctor can prescribe you.