The dying off is a just a natural progression of the flowering characteristics. They do not last forever ;-)) Your plant looks very healthy and happy and with no obvious insect issues. As noted above, a 3 y.o.climbing hydrangea already in flower is a rare and good thing!!

Except that it grew the flowers but did not bloom...

im sure whatever insects I saw on it ate the buds. Next year, I will spray it early. :)

It IS blooming! Climbing hydrangeas have lace cap type flowers, so a few large sterile flowers surrounding a cluster of tiny infertile ones. Just like your photo shows :-)

Here is another picture of an unnamed climbing hydrangea variety so you can see how it resembles your picture:

http://blumengardens.com/wp-content/uploads/2015/08/hydrangea-climbing.jpg

Please don't spray, and not as a preventative. There is nothing there to prevent, your hydrangea looks wonderfully healthy and has graced you with a few blooms at a young age. Normal blooms. These don't have the same showy display as some of the shrub types, there is no way to make it change flower type ;0)

"im sure whatever insects I saw on it ate the buds"

How do you know that? Guilt by association? How do you know whatever you saw wasn't keeping some other insect at bay? That the "sawdust" wasn't part of a bad insect?

Here's a cropped pic of my well established climber. Notice the sparsity of showy (sterile) flowers. It took about 8 years before the center (true) flowers came into their own and filled in. Ignore yours and it will thank you.

tj

Just what everyone else said. They are normal young climbing hydrangea blooms. They will get fuller but still be lacecap as it grows older. Mine was 7 years old before I saw a bloom, so yours is doing very well. Please don't spray as you can kill "good bugs" and there isn't a problem here, regardless.