Being two faced is an essential part of living a successful life.
There's another more positive term for the same thing. It's called "Being professional". Where you give all your customers the same high levels of service, regardless of what you think of them personally.
I would be a huge hypocrite if I criticised someone else for being two faced. When I am two faced myself.
However, having said that, part of "being professional" is keeping your negative thoughts to yourself. And not blabbing them on a group chat.
Your "friend" made a stupid blunder.
It's possible - depending on what they said and the context they said it in - that they may still like you. Just because you have some faults that they aired in a public place, doesn't mean to say that they hate you. They may still like you enough as a person to spend time with.
Although it's also possible that they hate your guts.
Either way, I wouldn't blame you if you treated them as an enemy for life now.
Expecting anyone to be a saint is unrealistic.
And there is a huge culture amongst teenaged schoolchildren to be negative and cynical about everything and to be positive about nothing.
But yes, the world would be a better place if more people focused on the positives and suppressed their thoughts on the negatives in other people.