それだけ　in this sentence? This is from a Manga, and I don't quite understand how the soredake in the 2nd bubble fits into it? But maybe I am completely off with the meaning of the sentences as a whole - so I've put what I think they mean in italics as well. Bubble 1: _I'd say I am a reserved (quiet/solemn) person, but_ Bubble 2: _I also watched Kou_ Does the soredake simply add an "only"? i.e. I also only watched Kou. Any pointers are much appreciated. Thank you!

> + Phrase or Mini-Sentence + / + /

would need to be remembered as a set phrase because it is a very common one. I means:

> "That is/proves (just) how much ~~~~."

Thus, the sentence in question means:

" ** _That is (just) how closely I was watching Kou._** "

Though there is not enough context provided, I would highly doubt that {} means "reserved, quiet, or solemn" here as you stated. I would think it is more like "slow" or "dull-witted".

Finally, regarding your translation of ....

I will not go into details as it is not part of your question, but you will need to learn not to use " ** _too_** " or " ** _also_** " in your translation every time you see because that is not what it always means. is an extremely nuanced particle.