Reminder the girls already lost their virginity to MC on chapter 18, anyone who still insist on this 'mc is a cuck', and 'it's ntr gaiz' BS are just ntr cuckfags trying to shit up the manga to impose their favorite fetish for that sweet daily dose of doom and gloom depression fix.
Also a reminder; said tentacle slime fuck scene is non-canon filler just like those one piece anime filler arcs.