Lee is right, a one-way written notice to the Realtor AND his/her Broker and you can move on. If the Realtor has a Buyer/Brokerage agreement with you and is the "procuring cause" (ie: he or she finds the property, shows it to you, and has proof through his or her SUPRA key that this was done); then he or she legally does have grounds to sue you for the commission, if you go around his/her back and purchase the property.
Will he or she?
Probably not. It would be up to the Broker of the Realtor's firm whether to pursue legal action, and unless you're buying into a multi-million dollar property - it would probably cost the company more money to sue you than they would get from the commission they're pursuing.
Does that mean everyone should ditch their Realtor after he or she spends hours upon hours researching and showing you property? No. If you continue to go out with the same Realtor weekend after weekend - heck, if you go out with your Realtor more than once or twice, and then decide you aren't impressed; then that's your bad decision. Take the time to get to know your Realtor, before you waste his/her time. We don't get paid until you close; no one likes to work for $0 an hour. It says a lot about you as an individual if you can sleep at night after screwing another person out of not only money, but their time -- that's something they'll never get back.
Lana, I know that's not something you would do - but since you aren't the only one reading and getting advice from this site, I had to put in my two cents...Good Luck and if you need any additional advice please don't hesitate to contact me personally.
Sarah Turner, Realtor
Sanctuary Real Estate