There are many articles and news about how facebook is doing negative affect on people's mood, anyone, not just those who suffer from depression.
And these people feel exactly how you explain, all the wedding, parties, fun and happy things. But no one post their unhappy things online, so you and others don't see it, but that doesn't mean those not so happy things don't exist.***

Facebook is such love and hate, it becomes part of our lives. Few people don't use it, (or they move on the twitter, instagram, that I don't know). For some people, they have to, may be they have a business, or may be they are a free lace wedding make up and hair stylist, then he /she is greatly depend on facebook for networking and spreading the news. Just remember the *** when you use it.

You can't expect everyone in the world to like you.
And for the people who said they hate you (doesn't matter why), well, it's more of their problem than yours, there's something in their life that they are not happy about or they are not happy with themselves. (that's what I've been told too, by a counsellor)