From what you've said, hannah, you have asked him how he felt, and he's told you those aren't feelings which he shares.
It isn't uncommon for romantic or sexual feelings to occur between step-siblings, but it is important to look at it realistically: he likely treats you like he does because of that sibling relationship, and that generally just isn't a sound ideal to hold others to.
Basically, I'd suggest you acknowledge what you feel (sounds like you have already), recognize those feelings, but also recognize that you need to pursue other relationships.
In terms of your parents, feelings aren't actions, they are just that: feelings. And as long as they remain just that, there really isn't anything to be angry with you for.
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