Yes! Actually if you start reading this one first before Passion, you'll get confused of why Xinlu was acting like a mad man at the beginning.
Xinlu wasn't that bad........... until Ilay came and something happened between them.
(spoilers below) no, raga is a decently independent story. the only thing you need to know about passion as it relates to raga is that xinlu and ilay (in the beginning of raga, at least) are both obsessed with taeui and are in competition with each other. since xinlu can't stand losing to someone, he constantly throws tantrums because hes "losing" taeui to ilay.
there's also some minor details about yuris work in t&r as well as the ongoing political situation in passion but it's mostly irrelevant to yuri and xinlus relationship.
Do I need to read Passion first before this? Ilay actions (based on what I have seen) kind of scares me... Also is Xinlu a bad guy with the same tendency as Ilay or he is worst? PLS HELP ME