Things get complicated when you're dealing with friends, as your line of thinking starts incorporating personal feelings along those of your business thinking. There's nothing wrong with this, its just that you want to protect your friendship along with advancing your business interests, you are trying to be a good friend.
My advice would be to be upfront with your friend (1st real estate agent) and all other real estate agents that you speak with and tell them that you have put the word out with multiple agents about your future purchase. This absolves you of any issues down the line as you are up front about where you're coming from.
On a different note, there is nothing wrong with working with multiple agents when looking to purchase a property unless you have signed exclusive with an agent. Just remember that different agents have access to different networks and can bring you deals that other real estate agents don't have access to.
Good luck, hope this helps.