I've honestly been reading it from way back, for years now, and there's been hints of Tomoko's gayness from way back in the beggining not only with Yuu either.
Something I remember is around chapter 50 or so. Tomoko at one point thinks Nemo is into her (this was from before they had become friends and before they had even gone on the field trip where she met Yuri and the gang) and when she finds out she misinterpreted what Nemo did as a romantic advance of sorts she felt betrayed, ran out of the bathroom in tears and then fell on her face and hurt her nose in a classic cringe Tomoko moment. This isn't the only example either, this has been there for a long time now.
It would feel like an extremely sudden development if it went Het out of the fucking left field. It would be a huge damn dissapointment in my opinion.