Well technically mizuho said herself, the reason she's with Ena because Ena love her not the other way round. I think even before that convsation with her little sister, Ena probably has notice it. It's a one sided love.
Ena on the other hand love Mizuho and the kind that do whatever she feels like - example, she kiss Mizuho right infront of her little sister eventhought they just met, agreed to crashed at mizuho's sister house ( surely it must be mizuho, the one suggested) or to suddenly buy a necklace for her girlfriend. Which I find it normal if you're in love with someone. But knowing the feeling is not mutual can be a burden.
So something like Mizuho not worried about her girlfriend went missing probably a big deal for Ena. She probably hope that Mizuho be a bit worried about her and go out to find her. But she didn't! So it can be emotional for Ena.
Another thing, it's Mizuho who suggest to go to work seperately. So Ena's uneasiness is completely understandable.
Oh well it's just what understand. I might be totally wrong.
I'm agreed on your interpretaion...Definitely makes sense.
I'm just wondering what this manga intended, though. Especially about the role of Mizuho's little sister. I'm still focused on her ex-bf and that lost strap thing...maybe this isn't big deal though.
Anyway, at this rate Ena and Mizuho will definitely gonna break up since Ena endures and at the same time burdening Mizuho in some aspects. However, Ena had tried to leave Mizuho before, based on the monologue that she left but came back again. Maybe some dramatic change may occure in next chapter, hopefully.
Still, this series became one of my best manga. Such story hasn't really dealt before, and the relationship of those three character is really something never seen before...the existence of the little sister. I'm looking forward to next chapter and even further. Thank you for scanlation! Love your work!