Honestly i think this is pretty messed up (ugh). Sensei couldn't even confess to Suzume when she asked if he loved her or not so he rejected her. However now that Mamamura and Suzume started dating Sensei really had to confess to her. Since he was jealous of them two dating each other Sensei regretted not confessing and all that stuff. Its best for Suzume to make up her mind on if she likes Mamamura or if she likes Sensei because if she continues like this all of them will eventually get hurt.
This is my opinion by the way if you have a different opinion I also respect that.
Im bad at english ik
Edit: I read the last chapter and Im glad they sorted things out.
D