There are varying degrees of grief (the end of a movie or show is obviously not the same as the death of a person), but many people do experience feelings of loss around different forms of media, such as the ending of a favorite show.

There is nothing wrong with you if you aren’t happy all the time. No one can be happy all the time. In fact, a temporary feeling of giddiness or being high on life is often mistaken for happiness. 

True happiness is more of an inner peace thing.

You should take exceptional measures to make your users happy. Your first users should feel that signing up with you was one of the best choices they ever made. Then think of new ways to delight them. You can provide a level of service no big company can.