I thought for a bit that there was going to be a love triangle, but it seems for now it's avoided. I saw Saeki as being peeved at not being told and chosen to be her support for the duration and not because she was jealous, well okay a bit jealous but not in the romantic sense. If she stays a friend it's going to be much better than if she was in love with Nanami. We'll see.
The pacing isn't weird at all. The ending of the first chapter (as someone pointed out) she confessed after she heard that there isn't anyone special to her, and she confessed (more or less). The second she kissed her because Yuu said that she likely wouldn't fall in love with anyone, and I imagine Nanami became scared. So far it's only been reactionary and as she said herself, she hasn't felt like this at all so it's probably because of that that the pacing 'seems rushed/weird'.
I relate to Yuu a bit though, I don't think I'll ever fall in love either so I'm curious how this will progress.