This might not be helpful, but it's what came to mind for me:
Family love is not the same as platonic love for a good friend. One's family contains people that you love because they are your family even if you have nothing in common with them and don't feel the kind of emotional connection you would feel with your own friends.
Would it be possible to regard him as you would a brother and/or tell him that you feel like he's a brother to you? Someone you consider family, but do not have platonic-friend-love for?
But if you regard him as more of a co-worker, then no, you can't lie to him and claim to feel sisterly love toward him. I guess I'm wondering if framing your relationship to him as brother-sisterly could be a goal to work toward? "I don't feel platonic love for you the same way I do for my best friends, but I want to regard you as a brother--someone who will be part of my family for the rest of my life." ??
Personally, I don't like my brother all that much, but I love him and always will. [Of course, I don't live with him and never would!]
Eh, I'm not sure this is helpful advice. Sounds like he has many issues.
Single, straight, female, solo, non-monogamous.