why is life so hard

I do not understand why life has to be so hard and i do not understand why people pretend to be happy when sometimes they are not really happy at all. I go onto facebook and everyones post says how great there life is however you know that behind the curtains there life is not at all perfect than whay act like it is so great. i am in a relationship where i fight all the time and it is abusing and i want out but i have a child which makes it worse and i do not want her to grow up around fighting but with money and times being tight i do not know what to do it is very very hard.