everything happens for a reason...but why?

Ladies! I'm feeling down in the dumps! I fully believe that everything happens for a reason and God puts people in and takes them out of your life for a reason. Now I'm not questioning God. But how come guys come and go, but there's one that sticks around and always comes back. Now I'm not saying always comes back, as in, he finds something else then comes back. It's he's continuously coming to me. But we're not together. I really like him, but Im beginning to think he's not good for me. But then I think of well, Why is he still around and the others not?