I put all of my self worth into my relationships. How can I learn to be comfortable when alone?

After a recent breakup, I have realized just how much of my own self worth I put into my relationships. I actively lost touch with myself and my own interests, and felt content just putting all of my time and energy into my partner. The primary reason for my breakup seems to be that my partner wanted to discover who she was outside of the relationship. She wants to spend more time alone, doing her hobbies, and with her friends without feeling like it would affect our relationship. She was feeling drained by what felt so normal/loving to me.

Even as the breakup was devastating, the first thing I felt inspired to do was download an app and meet my next partner. I feel so sad, bored, and lonely without having my girlfriend around. I have lost passion for my hobbies, and I feel nothing when I have spent time with friends. I have very rarely been single for the past 12 years, and I want to break this pattern.

I truly loved my girlfriend with my entire heart, and truly want what’s best for her. She is one of the kindest people I’ve ever met, and I‘m happy she was able to recognize her needs, and provide me with a new perspective that made me finally recognize how needy and emotional I can be.

How does one with attachment / codependency issues learn to be alone without being miserable? I am a very affectionate person, and it genuinely feels like my tank is slowly leaking when I don’t have a romantic partner nearby.

Any tips or personal insights are appreciated. Please note that I have already returned to therapy. I am just looking for any additional advice, thank you.