A word for feeling simultaneously happy & sad
Solution 1:
Bittersweet:
- producing or expressing a mixture of pain and pleasure: a movie with a bittersweet ending.
- pleasant but tinged with sadness.
- a bittersweet smile.
(TFD)
Solution 2:
While somewhat broader than happy/sad, you could say ambivalent.
Having mixed feelings or contradictory ideas about something or someone:
Some loved her, some hated her, few were ambivalent about her.
Solution 3:
The dictionary on my Mac defines rueful as
expressing sorrow or regret, especially in a wry or humorous way: she gave a rueful grin
which fits OP's sentence quite well.
Solution 4:
Melancholic! Bittersweet more exact.
Solution 5:
Not exactly what the OP's looking for but tragicomic also describes both happy and sad feelings at the same time.
Tragicomic (adj): Something that is tragicomic is both sad and amusing at the same time.
Example: This was a tragicomic story of human frailty.
— Collins dictionary
Or ambivalent.
Ambivalent (adj): Having mixed feelings or contradictory ideas about something or someone.
Example: an ambivalent attitude to Europe.
— Lexico