1. I think in this context it means “because”, on pair with 「から」 in the end.
2. I’d translate it as “Because at that time my father…”
3. I’d translate it as “Because was crying”.
4. I’d translate the whole sentence as “Because at that time… my father was crying”.
5. I think, those were happy tears for having such a son.
Seems I’ve managed to answer questions 1-4 more or less correctly.
As for fifth question – it’s a matter of opinion, although seeing the drama might clarify things.
Actually, this drama seems to be quite worth watching.
This reply was modified 4 years, 10 months ago by trunklayer.