Sister with boyfriend ⇐ Incest

[Anonymous]

Actually, I have already created a topic related to this earlier, but I would like to know the opinion from the other side.
Has anyone noticed a sister with a guy? What did you feel (or what do you think, if this did not actually happen), was there any anger or jealousy?
Well, or somehow your sister openly had sex in front of you, how did this happen?