I don't have to have fun to drink!
Some people drink to become sentimental and open up about their feeling to their friends. My former best friend lost his brother very young and only ever talked about it after a few drinks.
Why can't I use 'nevertheless' here, instead of however?
Sounds like quite a high register, but okay, added.
What a dark lesson...
When choosing the words in English to match the Polish, 'however' and 'but' are both present. 'But' is wrong and the correct sentence shows 'however'.
'however' is the main answer, but 'but' (:D) should have worked as well...
what about although?
No, that would be "chociaż" or "choć".
Why can't "gay" be used instead of "joyful"?
I think that nowadays it's really hard to interpret 'gay' as 'cheerful'. It's just a dated meaning.