Ori no Naka - Ch. 18 - My Life Is For...

[zerio]

I’m just spitballing here because of the flashbacks but I wonder if Yumezora is the plain girl he confessed to back in high school (through email lol) but he doesn’t know it yet because she got married so her last name is different.

He didn't confess to that girl (also it was middle school not high school). We know from narration he never mustered the courage to talk to her once.
This chapter is contrasting that moment in his life, when he almost tried to talk to her at graduation but couldn't, to the present when he finally pulled through and properly talked and confessed to Yumezora.

Also that girl's first name is Yumi, so we know it's not Yumezora, whose first name is Kuroko. Unless she changed that too, which I wouldn't put past her but I don't think that's what the manga is going for here.

Edit: I just realized you meant Hotta, not Yumi. In which case it is possible albeit unlikely.

I really doubt that because there are 3 years gap between Yumezora and Gomi.
The girls in the flashback seem to be classmates.
Even assuming their birthdays put them at 1st year and 3rd year (her in March and his in April), I doubt he was brave enough to approach someone outside his class.