My point, which I didn't explicitly make (passive aggressive on me!), is that you appear to be making excuses and reasons to explain their behavior. If you make it about 'you' - you're the reason they didn't want to invite your spouse - then perhaps their behavior is not so bad? And so you can tolerate it a bit more, a bit longer. If you see this tendency in yourself - and you very well may not - then be careful.
They didn't invite your wife because they don't like her. It's fine not to like her. Maybe she is not so likeable to many people. Clearly R and M clash in the personality department. But if they wanted you at the wedding (and I realize there is a possiblity they didn't want you there either - I think this is a slim possibility but, hey, been wrong before!) then R needed to be invited as well. To do otherwise is a shocking breech of polite behavior even in our more relaxed etiquette era. And so back to the dicky/douchy behavior...