Introverts are very observant people. They can read you like a book. If you think they didn't notice, they did. They just decided to keep quiet and avoid the drama.
Dad,
I wish I didn't have to work so hard for your love and approval. I wish you could have been less critical of yourself, so you could be more loving towards me.
Dad,
Today is a reminder of how you're not here anymore. I wish I could pick up the phone and call you. It's really hard to see everyone talk about their dad today. I miss you.
Introverts hate asking for help. For favours. For advise. Even when they're in pain. Even when they're suffering. They just can't. They bear it all alone. They bottle it all up. They're fiercely independent, but sometimes they need help too. But they just don't know how to ask.