I fluctuate on this issue, and in fact in life in general I struggle between believing in destiny and making your own fate. On the one hand, I've always felt that "everything happens for a reason," which implies that there is some sort of overall "plan" out there that we are following, and that unhappy situations are just parts of the plan that you don't yet understand. This would also imply that whoever you end up falling in love with (or whether you are alone for the rest of your life) is a part of that plan, and therefore there must be a person out there who you are destined to be with. Or there is nobody for you, because your destiny is to be alone.
On the other hand, I feel that life is what you make of it, and that there is no greater plan for any of us. We just react to individual situations and hope that our choices allow us to be happier and better people. When I'm in this mindset, I feel that it's possible for almost any two people to love each other, it just takes hard work and commitment. Sure, there are some basic requirements to be met, but as long as both people are willing to compromise on certain disagreements, they can learn to have a happy and successful relationship with each other. And this is true of anything in life - if you put in the work, things will happen for you.
So, I go between these two opinions every so often. I tend more toward the second one because I'm very practical and not a big romantic. But then sometimes there are certain things that happen in life, or certain timings, that make you think that it must
be more than coincidence. But then I remember that that isn't logical.
So in conclusion, I have no clue.