You didn’t plan on breaking his heart. You didn’t mean to make him fall for you and then force him out of your life. But it happened. It happened, and you feel absolutely horrible about it, even though you know it couldn’t have gone down any other way.
You don’t know how to explain it to him.
He’s never going to believe any those cliche lines about how you’re just not meant to be and how you hope you can stay friends. He’s going to think that he did something wrong–but he didn’t. You two just didn’t click the way that soulmates are meant to click. But that’s hard to explain in words. In fact, it’s not something you really can explain. It’s just something you feel. It sucks, because no matter what you say, you know you’re going to make him feel like crap.
You wonder if you’ll ever find love.
If you couldn’t make a relationship work with someone as sweet as him, then how are you ever going to make it work with anyone? Your guilt over breaking up with him will make you start to question whether you’re really meant to be in a relationship at all. Maybe you’re meant to be alone. Maybe you’re meant to spend the rest of your days in an empty house with no one around to make it feel like home.
You feel like a horrible person.
You know you’re going to be fine without him, but that’s the problem. In the past, you were the one crying into your pillowcase for months while your ex moved on in a week. But now, the tables have turned. That should make you feel powerful, but it just makes you feel shitty. You don’t want to be the person someone else is crying over. You wish he saw the relationship like you see it. You wish he would realize that you two just aren’t meant to be. It would make things a whole lot easier.
You feel like you did something wrong.
You didn’t mean to break his heart, but you did. Causing that much pain couldn’t have been an accident, so you’ll start doubting yourself. Did you lead him on for too long? Did you get too close too soon? Did you break up with him too harshly? There’s nothing wrong with dumping someone you don’t feel a real connection with, and you know that, but you still feel like a villain. You still feel like you could’ve done something to avoid hurting him so badly.
Relationships become more complicated.
In the past, you were worried about entering relationships, because you didn’t want some hot guy to break your heart. But now you have another problem to add to the list. Now, you have to worry about breaking the guy’s heart, too. But if you keep thinking about all of the things that could go wrong, you’ll end up walking on eggshells, and that’s no way to live your life. That’s no way to find true love. 
