You don't need to have the character act like a cheating douche lying through his teeth with the woman he's fucking.
Just the sex scenes are more intimate when done as a couple and not as a group, almost by definition of the word.
This MC is going to date every single woman, he will tell them all he loves them and how important they are to him. Not long after telling them that he'll go to another woman and say the exact same thing all the while never committing to a relationship with any of them.
This is why I don't like harems.
You can make the sex scenes as intimate as you like they are still superficial relationships with no romantic feeling to them.
The words are there but then they are said to someone else a few minutes later and these women that think they are loved sleep alone at night while the man that "loves" them is balls deep in someone else telling them just how important they are.
The only difference in this scenario is while those women are lying in bed alone every night they know he's with someone else, balls deep and saying the words he just said to them.
None of them will ever have a fulfilling relationship because he has to fit everyone in so it's a queue system and how romantic is that. Let's just hope there isn't more than 7 or they would be waiting longer than a week to get boned again.