In case you can’t understand, the first thing that Aoi Shouta says before he begins to sing is, “I’ll show you…”
It sound strange by itself, but as soon as he starts singing, the words he said line up with the actually beginning of the song, having it start off as, “I’ll show you a Monogram becoming one in two…”
Sorry I wasn’t able to crop out the beginning, but here it is!
If no one is sure what exactly Ai is saying to the audience, he’s basically saying that he’s very nervous to sing on stage. Getting asked ‘Why?’ (from the audience though it’s silent), Ai says he just wants to convey something that he’s had trouble with for so long, and then he confesses,
“I like you”
(to the audience), though in my opinion it can be interpreted as Ai saying that he likes his Significant other, AKA whoever in the audience is one of his fans and such but that’s just me)
However, he says after that no matter how he says it, it doesn’t come out the way he wants to, and that he hopes his song will convey what exactly he wants to express to everyone~