this manga by like this: "hi, i'm MC and I have a big 'duck'. If it move I must kill it or rape it in the name of justice or love... I can't be defeated because im the MC and I metioned i have a huge duck?"
Actual NTR happens, one of the harem cheats, full penetration/creampie etc. MC does nothing because he thinks it's his own fault for leaving her alone for too long. And you're pretty much correct with the ending.
The Perverted Guts (from BERSERK) who will conquer all women he likes in his endeavours to become a king.
Is actually the should be title for this series.