As far as I know though there isn't really a natural and unobtrusive way to say "I love this person purely platonically" in Japanese, so we can't exactly use that reasoning to say Bruno's feelings are implied to be way or the other. How would the novel have done this? Have Nemesis say, "He saved me because I'm the daughter of someone he loved but only as a friend"?
"Aisuru" is considered the "L" bomb. You don't say it to someone that you care about casually. However, it does not imply that you long for them romantically like you might a girlfriend or boyfriend (as "koisuru" would), and there are times when someone might use it to refer to their family or very close friends.
We know definitively that Bruno loved Gallerian in a serious way, a love that persisted through most of his life and gave him an unwavering dedication to him. But I don't think we have enough to say that he was homosexual and in love with him. I don't think we should be making an effort to somewhat impy it one way or the other on his article.
--Not to go on length about it but I just want to avoid any nuance kerfuffles.
However, the actual chapter where Bruno spares Nemesis is chapter 2, so perhaps we'll get something more certain when I'm done reading it.