Thanks for the chapter!
Not surprised MC doesn't have any friends considering how cold he is to everybody. Especially using items on women just for personal benefits without emotion or regard for their feelings like they're resources from a game. Probably why it never occurred to him the reason why the arrow didn't show any effect was Sensei was already madly in love with him, otherwise why would she agree to wear skirts for him, keep the dungeon a secret, and help him fight in it. Lucky for him Sensei couldn't read the writing but he really should stop fooling around with the items. Like using the armband in the dungeon was foolish as it made her aroused causing her to be distracted, unable to use full abilities in the battle, and burn through her stamina faster. Also, the more women he ensnares the higher the chances someone is going to get suspicious and investigate him, along with trouble arising when they find out about each other and either get angry with him and/or jealous of each other leading to infighting. Then there's the possibility of one of them having a diary or observant friend which brings the question up front why are they so attracted to him out of the blue or despite him doing this and that with others.