I think that you do have some sort of feelings for them. I'm not saying that you are outright in love with your friend, but it's totally understandable that you have some feelings for a guy friend and get a little jealous about it. I mean I have guy friends and I get a little jealous too sometimes. Of course, I don't find it too conflicting since I know that I don't like them that way and I know that it'll never be that way between us. But since you are finding those jealous feelings rather conflicting, you might want to reconsider exactly how you are feeling.
I can't tell you right now that this and this and this are what you are feeling and why. That is really up to you to find out. No one knows your feelings better than you do so that's why you'll have to do some introspection. But I'd honestly say that from your description and your conflicted feelings, that you do like them a bit more than just a friend which is perfectly normal. I mean it hasn't happened to me yet but I do know of people who have had this feeling.