And my definition? My personal opinion is that happiness depends on one's level of consciousness. In other words there's not one definition. One definition fits none.
Look at Maslow's hierarchy of needs. On the 'Physiological' level Epicurus' definition is valid: "The cry of the flesh bids us escape from hunger, thirst, and cold; for he who is free of these and expects to remain so might vie in happiness even with Zeus." On the level of 'Safety' I'm happy when there's peace in my part of the world, my job pays well, my own house needs no maintenance and my kids are doing well. Kate Bush's definition "loving and being loved" fits to the level of 'Love/ belonging'. When I write another nice blog that's received well, I'm happy on the level of 'Esteem'. Level of 'Self-actualization' is looking at life and planet Earth like this and this.
What makes me most happy? É simples: ter você.