The Reason Is - It Feels Good
The reason they come into your life is totally subjective to your state of mind and needs at the time. You're inviting them, or accepting them, into your life because you each fill whatever gaping hole you've got going on in your lives.
They guide you, appreciate you, show you insights you'd never see otherwise. They see your vulnerability. You see theirs. Do you take that vulnerability and use it to your benefit?
People come into your life. You love them, trust them, accept them and they see your sweetness and open up so you can pour it all inside them. And you do. You just pour and pour because it feels so good.