Well, we know what DPC did with the last threesome relationship. Question is, would they really have another one end badly?
I have my doubts that J&M relationship will survive Scavenger Week ... and when one of the girls is unhappy and mc comes along, she will likely move closer to him again for some comfort. (The same actually applied earlier for Josy and Maya when they were separated, for Sage after she was cheated by Chad and for lonely Isabella and Jill.)
It becomes more difficult if mc starts to date a girl like Jill or a couple like J&M in public and more or less becomes engaged with her/them. This would drive the other main LIs away and leave only the sidegirls like Quinn, Riona, Camila who enjoy non-committal sex and like to tease mc. MC on the other side would feel guilty for cheating and likely pass on further sexual opportunities which would mean the end of the game.
It's like juggling with several balls. Once you catch a ball to keep it, you likely loose the other balls. So for a game like BaDIK it is better to keep juggling with lots of sexy girls but not try to catch one of them.
Edit :
Most of the characters are just 18 or a few years older and some like mc, Josy, Maya and Derek are the first time away from their parental home which gives them opportunity to explore themselves and the (sexual) world around them without annoying adults. After escaping the parent-child-relationship they have to find out who they are and who they want to be and with whom they want to be. This usually includes a lot trial and error with different partners. Some romantic relationships don't work in everyday life. So I would not be too focused on relationships as long as the characters stay friends and do not permanently "close doors".
