On the dlsite website it says
" *There are multiple endings, but we will make it easy to choose.
**Included endings**
1. Both cuckolded END1 (called double cuckold)
2. Both cuckolded END2 (called double cuckold)
3. Only the heroine is cuckolded END
4. True END "
Ending 1 and 2 are determined by being double cuckolded (and cheating as the guy will lead to the girl being cuckolded also).
Ending 4 is determined by not cheating as the guy.
How does one get Ending 3? For context, I tried my best to avoid luna ntr but tried my best to get crone ntr (as I assume that's what the ending 3 would require)
EDIT: Looking through the recollection room, it appears that it should've been translated as "Only the hero gets cuckolded END"