She hasn't been doing it seriously since New Year's Eve (one of the "flags" she burned that night), but Anna doesn't know that and she's continued to be extremely worried about their casual interactions even after Yamada and Ichikawa begin dating.
She dragged Ichikawa with her to make chocolates at Yamada's place for valentines.
She also tried to cover by pretending they were dating.
If it wasnt for Sekine, Ichikawa wouldnt have went to Yamadas, and would have left asap once they met Yamadas mom.
Not only that, but the search for Kentarou (Anna's Akita dog keychain), she explicitly lied about intending to go over to Anna's so she could guide him in the right direction without him questioning it too much, and then made a plausible and over-dramatic excuse to go away once he was with Anna (who she was in contact with to make sure they'd meet up, at least in one version of this story, either the anime or the manga - I do know the anime just had her quietly walk away after checking her phone and seeing her conversation with Anna leading to them meeting instead of yelling a lie about her brother possibly dying in hospital- the anime being so much smoother of a move for her). I've even seen theories that Moeko (Sekine) was the one that hung Kentarou up on that tree for Kyo to find and score points. She might have even figured there's a possibility he'd end up taken back to Anna's place, but clearly not enough to not be surprised when Serina pointed out he behaved like he had been there already during the chocolate-making visit, probably because she had likely already assumed he hadn't been up there because she had to drag him back to the building entrance.
Just about every time, I've seen her sacrifice her own time, and chances with people she's been interested in (like Nanjou 'pickup-pai' Haruya), for the sake of their budding relationship.
Meanwhile, she's got a bit of a unintended drawing of interest from Adachi that she honestly doesn't seem all that concerned about right now, and even seems to find it amusing. I know some of the earlier volume extra arts (I don't know where exactly they are on the volumes/tankobons, but they're the second/third page on the volume extras here, after the actual cover art and before the really neat table of contents (the
skeuomorphism), such as
Ch30.5, Pg2 and
Ch44.5, Pg3) depict Adachi and Sekine, among the rest of the gang, hanging around each other more than they'd ever have done that early in the story, too, which felt to me like foreshadowing the current situation of him showing interest in her. It's a shame we don't have the later volumes' copies of the same pages, because I would love to see if that trend continued in Vol 4 and 5.
And that, at least in the anime
Sekine seems to mildly reciprocate the interest, at least in the form of some acknowledgement of respect or care for Adachi in the aftermath of his sports festival 'defeat'.