Fr, tho
Nope, it’s obvious that his love interest was Mitsuru….
Kaname hinted on it. He said when they’re still very young, Leo is more affectionate towards Mitsuru, but as they grew up more, Leo hardly dare looking towards Mitsuru’s way. I bet that’s because Leo start looking at Mitsuru as a man that he would attracted to.
And that make it obvious why Leo so insistent on not living with Mitsuru because Leo afraid of his feeling get discovered.
At that time, Leo still don’t know that they already know that they have no blood connection. Leo don’t want to feel guilty of loving someone (Mitsuru) who think of him as brother, and don’t want to get caught about his feeling.
.
I did not read the raw, I did not read spoilers, this is just my deductions from all the clues/hints I’ve seen so far.
Or, it could be the other way around…
Leo realised Mitsuru actually have feeling for him, or already confessed to him, either way, because of that, Leo try to avoid Mitsuru. And clinging to Kaname was just to make Mitsuru give up his feelings.
So yeah, I am certain that it’s either the case of Leo liking Mitsuru, or Mitsuru liking Leo.
I know they're supposed to brothers, but I can't help but think that Leo wants Kaname in a romantic sense... Maybe I've read too much yaoi and that line about them not being blood related doesn't help