Buying a home is different than buying a car. When you buy a car you are out for yourself and the salesperson is a mediator between the dealer and you. They have what is in their inventory to sell and that is it. If they don't have the model you want, they are out.
Your Real Estate Agent is in it for the long haul. There are many obstacles in buying a home and without an expert on your team, you may fall victim to some of these obstacles. The seller has a listing agent and their first obligation is the listing agreement they signed promising to get the best price for their seller.
When you enter into an agency relationship with your Realtor, they are working for you. They expect that they will be working for you throughout your home buying process. Buying a home could mean that you write up multiple offers, look at many different homes, and sometimes you get the first home that you look at.
Your Realtor understands this and from the minute you hire them, they have your interest in mind. When you have questions about a particular home you should call your agent to ask them. When you speak to another agent you should let them know that you have been working with someone else.
Be as loyal to your real estate agent as you expect them to be to you.