I don't succeed you said I can do what I want but still I get the same ending
Let me explain how the game works with the endings:
1- You become her slave (bad end). Can be triggered if you cum inside her if you don't reach the 4th heart (no dog ears/tail), past the 3rd day without do anything (dog ears/tail variation).
2- You become her husband (normal end). Cum inside her with 4 hearts.
3- She becomes your slave (masochist end). Use the collar in her when the 4 hearts have a purple color. This end have 2 variations depend if you remove the ears/tail cumming inside before the end of the third day.
Now how the hearts works... You can reach the 3rd one without problem, but in this point you must be a bit mean (saying sentences like "you'll become my pet" or "i'll punish you"). She reacts with a cross vein bubble (that meants you are doing well), mix those sentences with the kind ones and eventually you can unlock the 4th heart. When you have the fourth heart, just be mean all the time and slap her during the orgasms. Once the hearts are enough purple, use the collar and unlock the 3rd ending.
Tip: When you reach the 3rd heart you can present the collar, and next you say are not serious about it, that gives instantly the 4th heart, but blocks the masochist ending.
This answered your questions?