I had a quick look, but might be we're dealing with a condition that your stuck. It would be the first time I've heard of this.
I'll need to look at this in more depth.
To get you going I just increased the corruption of your savefile to 26 with save editor online so you should be able to do the old neighbor event now and gain some corruption there.
WoW! Thank you for your swift reply and for helping me on my way! Some things that may help you trace the issue:
1. It is a rather old savefile. I'm not sure in which version it started.
2. I don't have the pass for the massage solon yet. I had it some time previously, but later I started a new game and forgot where it was. I'd appreciate you to DM me to tell me. (Not here ofc, for people may consider it a spoiler).
3. Some other quests stay in my log without being able to progress. Like:
- meeting Gina in front of school. I also missed, therefore, the quest line where May applies for the cheerleader club

- training on the balcony, even though it only reduces my lust anymore,
- to go and work out at the gym, which I do, and I even work there for a while now.
- despite her high exhib level, she still can't decide to go without undies.
Almost finally, some things that you may want to look into in future versions:
- the save mechanism is very sluggish, and even though I disabled it, the game still auto-saves, or at least puts the 'last save' bar on it,
- when May goes to the shower naked, she still insists on going back to her room first to equip the bath towel.
- likewise, when May is naked before going to sleep, she still states that she needs to slip into her sleep attire first, even though that means: staying naked.
- in Mr. Stein's house, when she goes up the stairs, she continues to walk inside the walls.
- in the game menu (the Esc menu), the weekdays are typically shown wrong.
And
really finally for now: Thank you for this great game! There's only too few games like these that I, a hetero exhib minded woman, really enjoy playing. Keep up the great work!