Congrats to the team for completing this work.
When I'm not super satisfated with the ending it didn't go badly like Sundome or the other one with the dollmaker.
When it seems to hint to MC quickly passing his crush for the whole serie it could be taken as a moment of maturity with MC understanding that sensei was thinking of him even after she left.
And is not like they can't meet again after he graduates, the biggest reason for her leaving was really not continuing a relationship with a student...so when he graduate she could try to contact/check on MC, she got into the relationship, more than she wanted, and doesn't want to let it go, unliek other stories from this mangaka...there is a chance.