My interpretation is that Deido's love for Shinobu has absolutely nothing at all to do with sex or sexuality. To be honest, the closest textual evidence I can find to support your interpretation is the language modern Deido uses to describe her as "beautiful" and stuff. Other than that, their relationship is portrayed as completely wholesome. The fucked up bit isn't Deido's feelings for Shinobu, but the unfortunate circumstances surrounding her illness and death. And of course, the effect that had on Deido.