well, there was no chance to deepen and develop their love after all, it was too short. and i think it was more of shiki's personality to hide his deeper thoughts. he died happy. it was meant to be. but their love isn't.
more like it was set up as reiji found the one that was really for him. and katsura found his happiness. both looked at the present instead of wallowing in the past. they got the perfect closure.
some people find it hard to express their feelings. i personally did feel the love between. reiji loved him so much that his death haunted him and stayed with him. shiki loved him enough to visit and make sure he was okay. reijis love for shiki, doesnt diminish his love for naoya. =)
I must say I like shiki's personality to an extent but I didn't really feel the love between him and reiji. Shiki was too clingy in a way. I wasn't sure on reiji's feeling though. You get the parts where he's thinking about him but it just seems his love for naoya is so much more natural.