We are always changing as human beings. When you meet someone and start a romantic relationship with that person, you've clicked on a particular level. You compliment one another and everything is new and exciting. You're learning all about each other and finding ways that you are similar and ways that you're different. Building a romantic relationship takes time, but it can be rewarding to be with someone who is enthusiastic about you.
As time goes by, your relationship is tested when you clash with your partner. These differences of opinion can do one of two things: bring you closer together and strengthen your bond, which is awesome, or push you apart, which is not so awesome. If you find that you are disconnected emotionally from your partner, and you two are on the verge of separating, that can bring up feelings of sadness. This is where a difficult decision needs to be made. Here's the thing: you don't have to hate your partner to decide you want to break up. If you love something let it go. That means that if you value this relationship and want to honor what you had together, but you know it isn't working, it's okay to let go of it for now. Maybe you'll come back together or perhaps you won't, but you don't know that unless you have the strength to relinquish control over what "could" happen. Tell yourself it's okay to let go. Nothing terrible is going to happen if you decide to separate from a person that you once deeply loved and still do. Sure, it's brutal and heartbreaking but what is the alternative? Staying in a relationship that you're dissatisfied and unhappy with? I don't know about you, but I want to find happiness in my life and I'm thinking you do too.
Take the leap (as hard as it may seem) and let go of what was. It's not the same anymore. Human beings evolve and change and though we have a fundamental sense of self, that personality is ever-changing. When you are with someone, you either grow together or grow apart. Hopefully you evolve together as a couple, but that is unpredictable.
So, what happens if you have to let your relationship go? You survive and focus on yourself and healing. You find the things that you enjoy and do them. You hang out with your friends and you allow yourself time to cry your face off but you also keep it moving.
If possible, I recommend the "no contact" rule with your ex; this allows you to heal. Try to do this for a month at least. If you feel like reaching out to your ex, call/text a friend and tell that person what you intended to say to them. That way you get it out but you're not talking to your former partner.
Your life continues while you work through the pain. Eventually you will heal. Maybe that person will come back into your life or maybe they won't. Only time will reveal that.