The tl;dr is "Yui x Ritsu"
The slightly longer story is that if you watch K-On! while really trying to overinterpret every interaction and assume more stuff is happening off-screen, a few romantic dynamics develop, with Yui x Ritsu being the most obvious.
The full story is 13+ charts and an 8 page writeup that I did as a personal project to justify this overinterpretation. I may post it somewhere if I ever decide to clean it up and make it presentable to the public eye, but there's a lot in there. Ui x Nodoka. The Azusa->Yui->Ui and Jun->Mio->Azusa parallel. Yui-Mugi breakup arc. The Azusa human instrumentality arc.
My friends have called me schizophrenic for making these charts and while I don't agree with their non-clinical use of the word "schizophrenic", you should know that when I say "speculative / non-obvious" for K-On! in particular, it's at about that level of extreme interpretation.
"Learn" and "bird" are pronounced very differently depending on the accent of English. Wiktionary has "learn" RP pronunciation listed as lɜːn and American as lɝn, although personally I don't believe in ɝ so I would write it as lɹn and bɹd.
Slight rant about American English IPA, but Wiktionary even has American "bird" listed as bɜɹd, which is frankly ridiculous. Say bɜɹd out loud and it sounds absolutely insane. Be'rd. Nobody says bɜɹd, it's gotta be bɹd. English spelling treats R as a consonant, but American English functionally treats it like a vowel. If we spelled with R the same way it's pronounced, it would be brd, lrn, teachr, wrking, etc. Not suggesting a spelling reform, because the current system works so well for uniting different accents of English, but it seriously bugs me when people talk about how American R (ɹ) is a consonant. It's not!