If you can, say it.
If you can't, say it any way. It will be good for you to express it.

Here are some Father's Day thoughts from "What's your grief?" (www.whatsyourgrief.com).
This is "grief for the rest of us." That the way they describe their website and grief support tools.
I love their style, relatable approach and I respect their knowledge and writing skills at addressing the difficult subject of grief. Perhaps they will help people avoid grief less. The following is from a newsletter. If you search "Father's Day" on their website, you'll find a more articles and angles on grief around Father's Day.
"Father's Day Writing Prompts:
For anyone missing someone this Father's Day (or any day, really) and looking for some prompts to help your writing and reflection along.
Three things I wish you knew about my life now are . . .
One way you impacted me that I didn’t realize until after you were gone is . . .
When I think of you, the words, thoughts, and memories that first come to mind are . . .
The imprints you left on me that I would most like to affirm and develop are:
The imprints you left on me that I would most like to relinquish or change are:
I wish I’d had the chance to tell you . . .
If I could have added something to our relationship, it would have been _______ because:
If I could have removed something from our relationship it would have been ____ because:
One thing I am working on forgiving you for (or have forgiven you for) is . . .
One thing I am working on forgiving myself for about our relationship is . . .
If I had to sum up our relationship in three words they would be . . . ."
Healthy habits are essential.