Here is a quick 3-step strategy to memorizing any jazz standard: repetition, repetition, repetition. I mean....yes, and no. It is true that there is no substitute for repetition. That is a significant difference between great players and those that are less great - the amount of time dedicated to improving craft - and I don't think anyone has figured out how to do that without repetition. But it is the kind of repetition that you do which really matters. To be holistic in our understanding of tunes, we have to be holistic in how we come to understand those tunes. So yes we should have a lot of repetition, but not just of playing the tune.
Repeat your listening. Listen to the tune a lot. Find lots of recordings and take time to enjoy each one. Play the tune in the shower, when you are driving to work or school, when you are making dinner or reading at night. Take time to be intentional about what you are listening to. Be able to tell the difference between how one player plays the melody or improvises a solo versus another.
Repeat your singing. There really is no substitute for singing. Singing is the proof that we are internalizing the music. Can you sing the melody? Well, if you can't do that then there is literally no way you can play the melody by ear. Can you sing the roots? Or the 3rds and 7ths? Well, if you can't, then finding them on your instrument is an intellectual exercise rather than a musical one. Everything that you are listening to, sing along with as well! Sing along with your favorite arrangements. Sing their solos, sing the bass line, sing the roots of chords, sing your own solo.
Repeat your playing. The very first post in this series (Click Here) outlined a process for learning tunes. This is a tried and true, "coming of age" kind of process for jazz musicians to go through. It is the kind of practice that many of us think of when the idea of "tune learning" enters our consciousness. That process is most effective when it is repeated often.
My order above is intentional. If we are going to memorize tunes the process starts with a lot of listening, continues with a lot of singing, and then is transferred to the instrument. Of course repetition is the heart and soul of this- but if you are stuck, check yourself? Can you sing it? Can you hear it? You may find that answer to your challenges lies in the repetition that should occur off the instrument.