It sounds less like you’re missing your ex, and more like that you’re disappointed in the fact that the relationship failed. It sounds like you built up an expectation of your relationship with your ex, and when that ended up falling through, you feel let down. And it sounds like you can’t decide whether to put the blame on her or yourself.

If I’m reading that correctly, I think the best thing to do is to acknowledge this fact, that the issue is not that you’re missing the relationship, but that you’re struggling with the emotional letdown when your relationship ended up being less ideal than you initially planned. Because if you keep thinking that the issue is that you’re missing her subconsciously, you’re going to get led to the wrong solutions. For instance, putting blame on you or her isn’t going to solve the actual issue.

If we take this premise to be true, then I think addressing the real issue probably comes down to thinking about what your expectations were and thinking about how the relationship was never going to meet those expectations from the beginning (based on the examples that you gave). Ultimately, I don’t know your situation, and I’m not a therapist. But that’s my interpretation of what you wrote