Dolphin, I understand your being upset. I would be, too. From reading your post though, I wasn't quite sure what that status of your relationship is. You say you're not quite together, but not quite dating other people.
This lack of clarity about what your the relationship is can cause BIG problems. It could be that he is taking advantage of the situation since you're technically not together?
Regardless, your boyfriend sounds selfish. He's never met this woman yet he's going to plant himself at her house for 12 days because it saves him money? All the while knowing it makes you upset in the midst of trying to rekindle your relationship? If you are trying to rekindle, this should be his priority. He should be there with you trying to make things work.
I'd think very seriously about whether you want to marry this guy. How did he treat you during the 6 years you were together?
“Inside every cynical person, there is a disappointed idealist”--George Carlin