Sorry, but I can't resist just a little rant here. Whatever you say Mary Jane was to you before this, you obviously had a pretty good 'secondary' relationship here. Did Roni know?
There may have been no physical contact, but a relationship thats good enough to jump into and arrange visits in August is to my mind as much cheating as what you believe has been done by Roni.

Is this a case of a guilty conscience jumping to conclusions as a way to terminate the relationship anyway?

I'm sorry if Ive overstepped bounds here, but it seems theres more here than meets the eye.