I still find that to be an odd thing, because after getting into the throuple with M&J, the MC could have easily just been like, "well, now that's settled, I've got somewhere to be so I'll see you gals later", and then go off to meet Jade. Same with the Cathy thing, that it's odd why being with M&J means you can't have Cathy.
It's probably done this way to give people not on the M&J path alternate moments, i.e. a M&J sex scene on their path is a Jade or Cathy scene on the other path, but even so, I still don't see a reason, story-wise, that the MC couldn't still carry on doing things with them.
Before ep 5 I thought that maybe once the MC gets a chance to speak to Jade, he could convince her that it wasn't his fault for missing their rendezvous and to give him another chance. But after the auto-decline of Cathy in ep 5 I'm less confident of that happening, even with M&J basically giving him a free pass which would make him feel like he can carry on things with Jade and doesn't have to stop.