I've had quite a lot of people walk in and out of my life, and not just romantically but genuinely the one thing that I want for them is to be happy. Our own personal happiness is something that needs to be valued and not received by another. I'd always much rather someone leave my life in order to make themselves happier, than continue to be a part of my life because they 'think' it will make them happier.
I urge and speak quite passionately on this subject because I have seen people who are not happy with themselves or their current situation but express that they are happy because of someone who is influencing them.
I worry for those people as then when their influence (whether it be a partner, business associate, friend) leaves, this person crumbles. Invest into yourself, don't cling onto things that you think make you happy.
Become happy with the sunrise and how it makes you feel, the warmth of a summer's day, seeing your breathe on a cold winter's night. Become happy with who you are and what you are bringing to the world.
Then you need not cling to people, but you can love them so genuinely and freely and hopefully they shall love you back the same.