In the flashback it is shown that Masatsugu has ALWAYS felt attracted to Rei, and developed romantic feelings for him very early. This is why I think that he really is in love with Rei. However, he also feels guilty for what his father did to Rei and his sister, both of whom Matsunaga was closed to and wanted to protect. In short. Matsunaga follows Rei both both reasons: for love AND guilt.
Thank you for your reply. You have a point there.
But I think Masatsugu not only attracted to Rei, but also attracted to Hisako.
In Masatsugu's own words, Hisako and Rei were equally important to him. He was attracted to them and hoped to have a deep relationship with them. This is why I think his fleelings for them were not the love between men and women. That's not lust, but Masatsugu and Rei had sex finally. It's a misplaced emotion and distorted relationship.Their stories make me so sad.

Well,I wonder that dose Masatsugu loves Rei?Maybe it's just guilt ????
And Yukio love Hyoudo or Tetsu? I think he will end up with Tetsu.