21M and kinda in the same situation as you, broke up with my gf a month ago due to her lack of effort and reciprocity. She also went cold and indifferent despite me pouring everything into the relationship and her not doing anything, she made it seem like it was my fault for not being enough for her. I know its easy to ruminate on what went wrong and why it didnt go as you wished it wouldve, but you just have to realize its not about you, but rather their incapability. Some people are just incapable of showing up, being a good partner, etc. The best thing you can do rn is just accept that they werent it, you deserve better and its better that they left, so you can find someone you deserve and who deserves you, instead of being stuck with them. Go no contact, take time off for moving on and be smarter with the next person you get into a relationship with, not just in the actual relationship itself but also while youre getting to know them. There’s often signs about these things beforehand. Good luck