This is another classic MN's dilemma - which nearly always ends up with blaming (&/or taking it out) on the hapless man.
The OP was disinvited to the wedding, by the bride because the aunt & uncle (sister or brother & spouse) of her deceased mother didn't want the OP at the wedding or reception.
Despite this being a major slight to the DP by the bride's family, and the fact that was very upset about it(as the OP states), the hapless DP had to relay the news to the OP. (In all probability, he had made his feelings on the matter clear to the bride & possibly the horrid, bitter in laws, but it's the bride's call & he had to respect this regardless.) Further it took from his enjoyment of the special day for him & he ended up in tears in the day because of the heart felt, magnanimous text from the OP.
Despite all this many posters on here are calling him 'spineless', that he' didn't have the OP's back', or further out there again, that he 'must not have wanted the OP there' himself.
So the bride disinvites the OP, most probably cos the aunt (deceased Mum's sister), thereby by passing the DP's wishes, the DP had to relay the news and yet the OP is now reevaluating her relationship with the DP.
So what did the DP get out of all of this- insulted, plans ruined, tasked with a horrible, hard , thankless job, that he hated & didn't agree with, (informing the OP) his enjoyment of a special day ruined, & all because he was stuck in the middle of 3 women all at cross purposes!?!
P.s. If I were him, I might reevaluating his relationship with 2 of the 3 of them, and maybe 3 depending on how the 3rd reacts going forward to this one off event, where invites were ultimately decided by the bride, influenced by the aunt....