I think it’s also because he just kinda stops caring what will happen at that point, because he sees himself in the stalker. It’s like the stalker is the “bad” version of himself that he wants to get rid of, and he chooses to fight head rather than leave because seeking outside help would be like running away from his true (and rather pessimistic) feelings. Can’t say it’s the best decisions but it’s not exactly a surprising one. It’s not a situation where he is in control, even if he had that one moment of quick thinking in the last chapter. If he had been a fully logical person, he wouldn’t have chosen to confront the stalker directly in the first place, because from the very start it was a reckless and not exactly mature plan.