Umm, normally when a guy does this with me I let him know I have a girlfriend but I'm flattered.
*edit*this isn't a guarantee but....
Thought I'd add more, sounds to me like he's interested maybe. Saying people think he's Bi is a hint that he's not against it and is even typically an easy way to mention bi tendencies or at least a bi-curious nature. High-fiving when you give an answer they like is a flirtatious habit guys do with girls, nothing abnormal or patronizing about that typically either. Asking you to go shopping is a way to spend time together and get your opinion on what to wear, so he'll be in something you like(if it was clothes shopping, if not disregard).
Sounds like he's opening up to you and possibly seeing if you're interested. Feel it out, if you're interested maybe ask him to go do something like a hike or a walk in the park. But yea, sounds like a suitor to me!