I'm not surprised at all. I expected either she'd reject or the relationship would implode one way or another. I was more surprised when he actually went ahead and confessed. That took balls and his efforts to get closer to her and then confess are more than recognized here.
But yeh, hasegawa is done. Without her to hang on to, mc will most certainly fall for momo for sure now. I really ship mc with sakurai but these type of series usually have those girls who fill the role of 'unrequited love side character' to stay unrequited. I mean, it would be great if it worked out otherwise though since she's legitimately the best pick for mc. Momo is a great friend by now that is true without a doubt but as a gf I think sakurai is better for him.