Came across this topic, and it's somewhat close to my heart, so thought I'd weigh in a little. Don't want to direct anything too directly at OP, although I certainly do recognise his frustrations.
For myself, I've been in this city almost a decade and am about to leave. Meeting a wonderful partner was one of my key goals when I arrived here, and I thought the alternative/down-to-earth vibe was right up for my street. Also, the affordability, size, accessibility of the city.
This, sadly, did not at all work out. Now that I look back, it's pretty painful to think that if I'd found someone I might not have to leave, or at least wouldn't be making the move alone
Trying to be even about it, I can see many areas where I was responsible myself:
Was too keenly looking for "the one", to replace someone I'd regretted breaking up with years before. The problem there is it's better to meet "people", and let "a one" present themselves after you've got to know each other a bit
I let myself get involved with a few people who didn't have the same goals as me
When those didn't work out, I didn't stick to my guns, and got dragged into the hook-up scene, which caused me to get very jaded, which was a hole I then had to dig myself out of as well. AKA baggage.
It's not like I was living in a hole during this time! The number of people I know in this city is absurd, and it's a raw thought that I'll lose so many friends now that I'm leaving.
However, the "problem of Berlin" is one I've heard plenty of times, and entered into myself. So, there are a few issues in this city that I think don't help:
The very diversity and accessibility of the city does make committing to a relationship less attractive, and in fact unattractive to some. I think it's pretty sad that people might feel this way - a great partner should enhance your life, and not restrict you except for not wanting you to cheat on them
If either of the couple is into the party scene, this will not help!
Many people whether foreign or German do just pass through here for a few years. So why take the risk with something serious?
Being foreign is a tricky bind - I see lots of German men with foreign women, but not so often the other way. Ausländer couples would make sense, but you have to find someone who has compatible goals (here for a short time? hoping to stay longer term?)
Some of these issues become a feedback loop, unfortunately. Fresh-faced newcomer crashes into problematic resident. Gets issues, they rub off. Problem gets spread, cycle continues.
But my God what a wonderful city this is if you're lucky to have someone. There's so much to do, and such great access to mainland Europe
Anyway, that was a muse. The main advice I have for OP is to try somehow not to let those frustrations get to you. Don't become a jerk, stay away from hook-ups. Be the best version of yourself, and if something doesn't work out, bear in mind that you never have 100% of the story. Therefore, don't assume you weren't "good enough" - with the right person it's easy