Fact is, relationships are complicated and making the decision whether to stay or to leave is one of the most difficult choices we're asked to make. The important thing to understand is that there are many different kinds of love and not all of them contribute to a healthy, balanced relationship and life. Despite what we've all been told, there are certain kinds of love not worth fighting for.
To be under the impression that the perfect person will come along is to be under the impression that relationships do not take work. When, in fact, no relationship has ever worked without work itself. When I look around at my grandparents, or other couples who have been together for decades, I am often surprised by how different they are from each other. None of them will tell you that they have been married for 30+ years because the pieces just fell into place. None of them will tell you that they are free from fights, disagreements, or conflicts. None of them will tell you that they will stay together forever because, hey, it’s easy. None of them will tell you that they pledged their life to the other because being with them is sunshine and rainbows every single day.
Love takes constant hard work every single day. And if you're not ready to work for it, you're better off letting go.
Yes, love is patient and love is kind, but occasionally it is controlling and cruel. Sometimes it can be fickle and capricious, always coming and going without delivering a thing you can depend on or be sure of. The concept that the only "real" kind of love is steady, simple, and passionate is a misconception at best and damaging at worst - if you choose to believe that anything less than perfect isn't love you're certainly going to live a hollow and lonely life. Instead, learn how to recognize the downfalls and difficulties in your relationship and differentiate between those you can fix, those you can't, and those you are willing to put up with. Only then can you make an enlightened decision on what is best for you.
Remember, regardless of how unhappy the relationship makes you feel, your fear of letting go is valid and nothing to be ashamed of. Because no matter how badly you are being treated, it still hurts like hell to leave. No matter how monotonous and uninspiring the relationship, it will still feel impossible to replace. You will still miss them long after you're gone, regardless of the circumstances of your departure.
But that doesn't mean you've got to hold on, that it's worth all the sacrifice, that it's worth a life. When heart and loyalty have given way to jealousy and mistrust. When passion is replaced with predictability and routine. When love becomes more about hanging on than making each other happy, it's time to let go and move on.