Without context, I can't figure out the subject for ケンカができたとしても. Is it 俺?
And 手が出せない literally means "It is beyond my reach." Without context again, all I can guess is that he has some reason to stay away from the incidence.
* revised *
I am adding a translation in a interlinear fashion, as the context is given.
Though I have been dating 美桜 (Mio?) for a long time, I have never had a quarrel nor a dispute with her.
Rather (Caveat: I have no idea why this "rather" is inserted by the original authour.) I would like to ask someone how I can have a quarrel with her, given her personality.
Even if I could, I would not lift my hand against her.
* Added (again) *
Of course it's partly because she is a lady (in the sense of "woman"), but there is another reason I can't do that.
(曲がりなりにも literally means "though imperfectly" or "in the fashion which is not satisfactory". This usage, together with the usage of むしろ, is the reason why I say "sloppy.")