My (29F) bayoyfriend (25M) is writing a "breakout" song and it's terrible

AMy boyfriend has been using this free time to write what he hopes will be a viral song that propels him to stardom. The issue is that he's played me the demo and it's just awful.

He is an amazing writer, and I've heard some songs he's written in the past that sounded really good. However, this time he's so dead-set on writing something that's outside the box, that he's essentially written the song version of a compilation video.

There's an operatic harmony, a grungy punk rock bit, even a bit of sax makes it's way in at one point (he doesn't play the sax, just has it on his keyboard). It's all over the place.

I have gently told him that the song does not tonally make sense (of course I've avoided outright saying it sounds bad), and I've also tried to tell him what parts I think don't work and which parts do. He will either tell me that I just don't understand music or will get really bummed out and stop working.

He also wants me to help him make his music video, and while I'd like more experience filmmaking, some of his ideas are just as incomprehensible as his song. What can I do?

TL;DR: *My boyfriend made a really bad song. I can only give so much constructive criticism before I start to look like an unsupportive girlfriend. He also wants me to help him make a music video which has unfeasible ideas.*