Hey SkyBlue…I understand you feel bad about this, I also used to feel much frustration in the past and I much felt the struggle.
What helped me hugely was to build a skill-oriented mindset and focus on the skills more than on songs: this way songs became just a mean to develop my skills and not the goal…I know! This sounds weird! But what do I do, I wasn’t able to play songs…there was too much going on for my poor little brain! It’s clear that in the end being able to play songs is what we all aim to!
As regards Happy Birthday…It seems to me you really want to be able to play it, otherwise you wouldn’t have persisted this much. A chord melody is a complex thing. My suggestion is to approach it differently…start from the Melody line only and add the chords when you are super confident with that. This was my approach
I love chord melodies deeply and I put so much effort and time into developing the skills for playing them…so I hope you’ll take my suggestion into consideration.