I still dont understand what the fuck is happening in this series
Basically Mari kept triggering Sensei to go "erotic 😭" in some shape or form and due to him being not wanting to act on his urges, created a cognitive dissonance episode in him so great he couldn't handle it and felt the only way to escape was to kill himself. Every time he did, it essentially reset the timeline to the beginning of the day where this started and Mari was the only one that was experiencing it. Eventually Mari figured out through a flashback that the only way to stop the loop and save Sensei was to prevent any chance of him becoming even remotely 😭 towards her.
Alternatively, you can sort of interpret it as Mari havng some sort of recurring nightmare/mental breakdown about her going "erotic sensei 😭" and being able to deal with the cognitive dissonance between that and treating Sensei as a teacher, and this panel is her accepting her own lewdness. This interpretation makes Mari a tad bit schizo imagining Sensei wanting to kill himself and failing to save him, but it seems like she got better. Hopefully.
You're too fast.... Sensei....Forgive me, Mari...........Fufu.Please wait for me, Sensei.I'll definitely become someone worthy of being by your side...*bang*