(The words below aren't mine; they're part of Seven Answers).
A few years ago I decided to end the long term relationship I'd been in for eight years. It probably took a year to make the decision and I fought it all the way. Up until then I'd been an easy going, go-with-the-flow, take things as they come sort of person, never wanted to make waves or upset anyone. But all of a sudden I found myself liking myself less and less and doing things I couldn't believe I was doing, avoiding the reality that what was wrong was that we were no longer happy together. But to solve the problem would mean making one person, my partner, unhappy.
In the end I had to do it, even though it was hard (as we talked and I told him, my physical reaction was extreme, shaking, crying, a real adrenaline surge). Afterwards I felt so elated and the months after were some of the happiest of my life.
The experience made me realise that to make people happy to have to be honest with yourself first, then think about others. That life is better when you really take part in it - it's messy but then that's half the experience. I'm a much stronger person as a result.