OH! Okay now I understand what happened. I need to change the text on that A/N. Activating that dialogue doesn't necessarily 'lock-in' Milo's ending, it just prevents you from getting Samson's ending from that point on.
Both Milo and Samson's endings have a two part ending dialogue in which you have to do something in between those conversations.
Since you saved after having seen the "Milo's secret stash" dialogue, he should have still been gone when you reloaded :/ The load/save feature is something I programmed so hearing about these bugs are super helpful! I just recently learned a new way to control Script execution order within the Unity engine that I want to try out to see if I can control some bugs. (But also I suspect this is moreso tied in with faulty logic at the tail end of the game. I'll look again at my reset script.)
Here's a non spoiler hint about how to get all of Milo's ending -- Find a use for what you discovered in Milo's final conversation.
And then here's a spoiler version of it:
To get his ending you also have had to be talking to Ms. Leith in the Casino to get her full dialogue. She will mention 'paying any amount of Chollars to best her fashion rival'.
After the Blood Moon, talk to Milo to lock you out of Samson's ending (again, apologies I need to rewrite this A/N) and be shown his 'secret stash' in the bushes in the backyard.
Nico will mention trying to find a use for all the bones and at the end of the dialogue they will either mention "I dont have enough information to know what to do with these bones" (this means you haven't seen the convo with Ms. Leith yet) or "Maybe I can turn this around somehow" (means you have seen the dialogue).
Go to Ms. Leith in the Casino and talk to her and it will trigger the very ending of Milo's ending.
Hope that helps and also thank you so much for letting me know about the bugs!