I'm upset with my boyfriend for behaving in ways I don't think are appropriate around my 3-year-old son
What innappropriate actions has your boyfriend taken around your son?
He recently showed my son how to properly smoke a cigarette.
You have every right to be upset about this, and I agree with you wholeheartedly. If you don't confront the boyfriend then he will demonstrate more in front of your son, he is just a bad influence on him. Set him straight and give him an ultimatum.
I know my boyfriend is a bad influence on my son but I'm having a hard time letting him go.
It's best to consider what is right for your child, not for your relationship. You have a duty to protect your child from negative influences.