I would at best agree that Julian was whatever the LGBTfhjfhsedhkfrh term for "He would fuck people of multiple genders if he at least thought that he had a chance with them," but I never saw any evidence of him flirting back with Garak. But yeah, I agree he was at least a bit bisexual. He definitely wanted Miles by the end of the show, but he was also clearly thirsty for Dax, both of them. He even ended up with Ezri.
The only thing I'm not really sure about was if Miles ever truly wanted him back... My gut feeling is no, but then again, I'm not married to Keiko...