If we think in the context of the MC, he is not waiting for either one of them. He is simply going to go about his days in college as normal, maybe continuing his relationships with other girls and doing his best to accept the situation with M&J. On that path, we'll probably see the occasional interaction with M&J, strained though it may be due to the feelings of the characters, and it will likely be amicable if not at the level of close friends. They may have the odd chat where he may learn how things are with their relationship and offer words of support, advice, encouragement, etc, or perhaps be indifferent and offer nothing as what he says could come down to player choice.
Should something happen between M&J and one or both of them come running to him for the same reasons they did before, then it will again likely be down to player choice whether to accept or deny any advancement they make towards him. Allowing it might not seem "noble", but it will come down to how DPC chooses to write this. If it's purely a moment of fleeting emotion, then the MC could be seen to be in the wrong for allowing it as it could cause more harm than good, but if the MC has interactions with them on the friendly side that have shown something to develop between them, then it may be slightly better as it's not resulting from raw emotions and/or lust, but from something deeper that has developed and so it feels more meaningful and justified.
Someone may end up getting hurt, but that is to price to pay when a relationship breaks up and so it's somewhat unavoidable in this instance if people want a solo ending for one of these girls, but it can be mitigated depending on their feelings about each other and the situation they're in.
