Why was it that Bloodraven was loyal to Daeron? Was Daeron the brother he loved?

Re your first question: I think I’ve discussed this before (check the archives, or the guest appearances I did on History of Westeros), but I think it was a combination of any number of the following factors:

1. Bloodraven agreed with Daeron’s politics/thought that Daeron was the better administrator.
2. Bloodraven thought that disinheriting Daeron and ending the legitimate male line of House Targaryen was dangerous and destabilizing.
3. Bloodraven did not want Bittersteel anywhere near government.
4. Boodraven owed Daeron for protecting him and his mother at court when he was a child, so was returning the favor.
5. Boodraven saw a chance for advancement under Daeron, parlaying his support into becoming Master of Whispers and other offices.

Re your second question: no, I think it works better if he loved Daemon but fought against him.