Boyfriend is one of the most difficult terms to define in the gay world. For myself I think of it as exclusive dating, short of living together and intermingling your finances & possessions, and having legal documents drawn, as partners/husbands do.
I've had some guys I considered to be a BF, but they wouldn't let me use the term; it spooked them because of the perceived commitment. And they didn't want to surrender the option to mess around with other guys, whereas I never involved myself with others when I felt I had a BF.
We'd go to movies together exclusively, and always just us when clubbing, dancing, to restaurants, taking out of town trips, etc. I'd think we were BFs, but I guess their vision was more FWB.
So I learned not to use the BF term because of guys who might be scared off by it, or the "L" word for that matter. And I never knew who they might be, so I'd say nothing. Until one day my late partner, and now my current partner years later, each asked me to marry them (in the non-legal sense allowed to us). So that I sorta skipped over the BF stage completely, and went from dating direct to partner. It worked out OK.