People meet, fall in love, have affairs, leave their spouses for someone else all the time. Doesn't matter the circumstances of how they met or know each other, it happens.
Brady & Nicole are very good friends, have been for years. Brady was at the launch, talked with Nicole, and knows she has been in Theresa's corner, and also that Kate was not. Please know I don't particularly like Theresa & Brady as a couple, but for all we know, Nicole comes to see Brady, talks to him, which is why he might have a dream.
Brady was just asked to be best man for Daniel's wedding before the crash.
We all have weird dreams, and no idea why, so I would not read anything more into that "spoiler" than the fact that Brady has an odd dream and Nicole is in it.
And yes, it is apparent that Brady will be getting the heart, while perhaps Eric will get medication that will deal with his infection/inflammation. He could be left with a heart problem of some sort.