What a horrible position to be put in. You are NTA at all though! You did something that I don't think a lot of people would have done, which is to ease the mind of a panicked bride freaking out over something she overlooked (boy is she a drama queen!) I would normally expect the resulting Reddit to be very different from this. You saved yourself, the bride and groom, the wedding party and the guests a lot of grief by staying clear-headed and coming up with a solution that shames no one. You could have clued the boyfriend in on it - I probably would have been inclined to - but on the other hand, his response to your incredibly kind gesture indicates that his reaction might have been one that would have completely destroyed the intent. This is probably going to get back to the bride and she may very well take up for you and tell him to get bent - so stay tuned lol!