I think that Deidara had a crush on Sasori, because: 1) He really admired him and called him danna as a way of showing respect.
2) When Sasori died, he became depressive and started to feel lonely.
3) When he committed suicide during Sasuke’s fight, one of the main reasons why he did it was because he didn’t wanted to live without him.
4) When Sasori was diying, he shouted that he was abandoning him again.
5) Deidara’s lasts words were Sasori’s definition of art, which means that he’s last thoughts were for his Danna.
6) It’s confirmed by Kishimoto that both Sasori and Deidara had a thing for each other.
Hope this is useful :)
