Why was it so emotional

When the Zoom play that my son was in last week ended and one by one all the parents starting popping into the screen to applaud? Oh look, there's that parent of that kid we haven't seen in years. And look! It's the mom we see everywhere, waving and smiling with her other 4 kids in her cheering section and wow, that must be the dad.

And there...is it? It is! Sure enough, materializing out of the darkness is my son's dad, Dada, all smiling and waving "yaaaaaaaay" the same way he did when J took his first step and said "dada" and ate his first Cheerio or smiled the real deal smile, not just the gassy reflexive one, but he cheered for that one too, or when he took his first drink out of a sippy cup, clumsily grasping it for the first time in his little dollhouse hands,  and all the faithful, level applause and cheer he surrendered on the bleachers at baseball, 4 rows back at the piano recital, from the curb when J stepped off the bus for the first few times or from the top of the steps, beneath the basketball hoop, in the soccer goal, on the sidelines, , catching the ball, on the ice, fork and knife, the first time he made a streak of purple across the blank page, pressed the Up button on the elevator, turned off the light, closed the lid, wrote his name, waved bye bye
Bye bye 
                Bye bye
                                bye bye
and said nightnight nightnight nightnight or sang Heeeeey Jude
or rang the bell for trick or treat or said thank you or gave a big big big hug to aunty or pet the cat nicely or ate all his peas or slept in his own bed or had his first sleep over or picked up a bug and cradled it to his heart like a prayer or so so so many things that it becomes a whirl of love all that applause as if it was his only commitment in life, to be there cheering and waving whenever J entered the scene, that no wonder it hurts like it does

And there he was at the end of the play, sure enough, waiting across town, out of the darkness and into the light of the theater smiling and waving his arms as though he'd been waiting his whole life for only this