I don't think he'd care.

I’ve bet Dustin will accept that Robin is a lesbian! Even though he ships Steve to be with Robin or I think Steve told Dustin about her sexuality before or after the end of season three. I mean Dustin should know about her sexuality by Steve since he is his best friend also accepts about Robin and her sexuality.

Right. What else would happen? Dustin doesn't seem the homophobic type.

Probably something nice and sweet like "Well I accept you for who you are". With that adorable dustin smile.

Totally supportive

he would support her all the way:’)

I think hed be chill bout it