It depends on what type of person they are, I mean if they only believe in certain sexualities because they just don't know any better then maybe coming out to them + teaching them a little more about sexuality would be a good thing.

But if they're homophobic, or know about these things but still think about him with contempt, then maybe coming out to them isn't such a good idea. Maybe introducing them to ideas slowly and coming out at a later date would be better. Bring up these topics and if they start being homophobic then explain why what they're saying is wrong. After they've gotten used to it then coming out would be a lot safer.

Coming out isn't mandatory, but do what you think is best.

Stay safe
el