How to prepare myself to be single 😭

First real relationship. One beautiful year. Ups and downs, but mostly ups. Promises of kids and marriage but I don’t think that is going to happen. He’s tired of me I can just tell. It’s my fault. All I do is pick and pick and pick at stuff. I ruined the best thing that ever happened to me. Only man who will ever love me and I made him stop. He says he wants this, but there’s just something so different I know he’s done or soon to be done. We live together and I just never felt this way about anyone and the thought of losing him makes me bawl my eyes out. How do I prepare myself to be alone again? I was so used to it and now I hate the thought of spending a day without him. But I don’t want to lose myself when he is gone. It is what it is and I can’t let anyone else bullshit hinder me as a woman which is exactly what got me in this predicament😭😭. How do you be alone after thinking you found your life partner?