LITERALLY NOBODY UNDERSTANDS THE CONCEPT OF OPEN RELATIONSHIPS
I reply to both of you. This isn't a depiction of an open relationship at all. I don't know much about it, but you just have to do a quick research on the internet and you'll find out that: "an open relationship is a relationship in which BOTH partners gave their consent to explore other options outside of monogamy: from the introduction of new sexual partners into the couple, to MUTUAL permission to see other people separately."
This guy in the manga never cared at all about the girls he dated, not in a romantic way, not in any other way. He basically just wanted to collect f*ck buddies. The girls were probably into it at first because he was never really clear about his intentions, he "trapped" them with the premise of being in a relationship and they obviously hoped to make him fall in love with them, so it inevitably ended badly every time. And coincidence, when he fell in love with Kaede he suddenly became monogamous... Truth is, he's never been for open relationships. When you're in an open relationship it's still assumed that you're in love with your partner and are considered of their needs. He just wanted to f*ck around basically. That's why people call him an a**hole.
He literally set all his boundaries to his partners and was very clear abt everything. Why they agreeing to date him if they know they’re gonna cross it and get upset w him