Yes I've had problems with one of my girls, in that I had an agreement she'd contact me once a week & she hasn't been doing it.
A D/s relationship requires a level of commitment part of which is regular time together. It's something you have to work out between yourselves.
BBW, there's a lot you're not happy about in this relationship, but no facts & figures are going to help you. It's something you have to work out between yourselves.
Even the sex thing- there's no rules for it, it's just what you & your Master agree on.
One thing you say, if I understand correctly is that he makes a time for a session, & just doesn't appear, even to give an excuse? If so that's unforgivable as well you know.
Only one thing is important- what you want.
Good luck, hope it goes well. Let us know how you go please.
Tojo