구나 느끼다

realise, it dawns on you, that…

"-구나" is the ending for something just dawning on you, and putting it in front of 느끼다 "feel" reports that moment: that's when I felt you were interested in languages, I felt there were so many stories I had to tell you, hearing the cicadas I felt summer had come, I felt this is a country with a lot of warmth. The -구나 keeps the flavour of a fresh realisation, which plain -다 느끼다 does not — that one just reports what you thought.