To everyone on the timeline saying wedding!Dream didn't do anything wrong... He got flowers on the SMP saying George would love them, implying that they were meant for him originally. When he was caught by Fundy and questioned about it, Dream said he "misspoke" and gifted them to Fundy instead. After that, however, he then turned around to get another bouquet in secret and told Niki not to tell Fundy.
The bouquet he had in the pictures showing off his dress meant infidelity, and he was looking in George's direction repeatedly during the wedding. When it comes to exes or past crushes, love can be messy and sometimes it's hard figuring things out, but Dream's biggest downfall with that was not being firm in his choices.
Personally, I think Dream still loved George and had wanted to be with him, but when his affections weren't originally returned, he moved on with Fundy. George then realized he messed up and wanted Dream back, but the wedding was already happening, so he objected and tried to show Dream he was serious about them now. But what the hell was Dream supposed to do with that - the objection, the kiss, the "It was what I had to do." - out of the blue and in the middle of his wedding to another man no less?
Yeah maybe part of him still wanted to be with George yet, but he had missed his chance, and now Fundy was in the equation showing him all the love he wanted... But did Dream really want to marry him because he loved him, or was he just looking for a way not to be lonely like he hinted at being during the date?
Of course Dream ran away in the end, he was probably confused as all hell as to what he was going to do with his heart being pulled every which way. And to be put on the spot about his absolute mess of feelings about the situation in front of everyone too? Runaway bride Dream was practically a given in that scenario.
After all, what other choice did he have until he could clear his head and properly explain both to himself and everyone else what was going on?
TLDR: Dream was a victim in his own right during the wedding by being humiliated for not knowing and fully understanding his feelings and being put on the spot about them. However, he also kinda brought it on himself by being wishy-washy on who he was choosing and it resulted in him being put in that position again. Love is messy and complicated sometimes.