Tbf, coming out is never easy and the closer you are to someone, the harder it is because there's the fear they may reject you. Family is even harder because even if they do reject you, you're still tied to them through blood bonds. It's actually easier to come out to strangers because if they have an issue with your sexuality, no skin off your nose (unless they get violent and harass you, ofc...)
So while it turned out to be a nothing burger, that doesn't invalid their hesitation to come out. The fact they waited for graduation to do so is logical in that regard : they're going to different school, so if they react poorly to the coming out, it'll hurt, they'll lose their friends, but at least they won't have to see them every day in class (where they might end up harrassing them, directly or by spreading the news to others).
You may think it's easier nowadays, where being gay is more accepted, but there are still a lot of people against it, unfortunately, so that's still a big hurdle to clear...
