Hey! Here are some hints.
Ending 2:
Do NOT buy him any tea at the kiosk (go straight home), don't sneak into the lab
When he interrogates you in the kitchen, tell only the truth.
Go into his laboratory with him.
When he gives you his creepy proposal, refuse him and say: "I don't want...".
Ending 3:
Again, do NOT buy him any tea at the kiosk, don't sneak into lab
This time, when he questions you, lie to him and then tell the truth.
Enter the laboratory.
When he offers the proposal, accept it and choose: "Yes, we will be together forever!".
Ending 10:
This one triggers automatically, just press start and watch~