Unfortunately, we live in a society that assumes everyone is straight until it's proven otherwise. Even though I'd argue our society is getting more and more progressive, our mindset on sexuality is something that is SO stuck in the past. Just because someone is dating someone of the opposite sex, hasn't shared a coming out statement, or doesn't look like a "stereotypically gay" does NOT mean they're straight. In order for us to be more accepting, we have GOT to kill this toxic mindset.
10 million American adults identify as a member of the LGBT+ community. Millenials identify more frequently as members of the LGBT+ community than other generation, so it's a lot more common now that the people you meet are NOT going to be straight. Remember - just because you're straight and just because the people you surround yourself with are all straight does not mean every single person you're ever going to come across will be straight, too. That's the definition of being close-minded, my friend. Friend groups have a lot more than just the one token gay friend - a lot of the time there are plenty of LGBT friends, they just may not be as open about it. And that's okay! No one owes you a coming out statement.
However, many of us believe that individuals in the LGBT+ community DO owe us a coming out story. And many times, this is what those individuals have to do. Their coming out stories are usually highly dramatic, full of tears and lost relationships with friends and family all over their sexuality. If we stopped putting the blank assumption on everyone we meet from the day they are born—yes, I'm coming at all of you parents who call your two-month-old son a "ladies' man"—coming out wouldn't be nearly as difficult for LGBT+ individuals.
There are so many sexualities someone could identify as, many of which fall under the LGBT+ umbrella. Yes, being straight is still much more common than not, but that doesn't mean we need to be heteronormative. We need to be more accepting, keep an open mind, and remember that assuming everyone we meet is straight or cisgender until proven otherwise is NOT okay.