To unlock each ending, you must finish the game a certain way. For ending H, you'll need to:
Optional: You can start at Bracciano (level 2 below)
Level 1 - Keep right.
Intermission 1 - Nothing.
Level 2 - Win or Lose the race, keeping right.
Intermission 2 - Leave Olga ("better to be apart").
Level 3 - Drive slowly so you will have time to trigger all of these conversation topics:
So… What brought you on the Via Aurelia?
How intriguing. Is this person a "she"?
…Oh. Where does she live?
Do you visit her often?
Ten years… That's quite a long time.
Tell me, Padre—where exactly is this nursing home?
Padre… Where is your mother staying?
Why, Padre? (Important! "What?" fails the questline)
That's just one more reason to visit. (Important)
Well, if that is what you truly feel. But…
But you would be with her, nonetheless.
You don't have to forgive. Just be there.
Who cares? You're still a man, Padre. (Important)
Alright, so where is this nursing home? - edoLocationReveal Trigger
Alright, Padre.
After this set of conversation topics, stop at the Nursing House (It has a red cross on the roof of the building and parking space in front of it)
Finale - Nothing.
Video courtesy of Dernop