@Cal C. The short of it is that you probably need a new agent. It sounds like you've been pretty clear with your intentions as you have 3 other properties under contract with the agent already. Very unprofessional and unwarranted on the agent's part. If this was the first time you were working with this agent, I'd be a bit more sympathetic towards them. From an agent's perspective, I've been on the other end when the listing agent absolutely lights me up for the offer you've submitted and insists on never working with you again. This is a legitimate concern of realtors. In smaller communities, this is particularly troublesome because more often than not, the same buyers and sellers agents are interacting quite frequently. Fortunately, I'm in Chicago, a big enough city where I'm less likely to run into the same agent multiple times (although I have) and because my brokerage business is my "second job,' I have no shame in submitting anything for anyone. I've come to learn that with respect to anything in life, it doesn't hurt to ask.
I do agree with @Adam Bartomeo. So many realtors are very unprofessional and are very unethical, not to mention lazy. In many cases, it's amazing how many times I have to contact a listing agent to have a potential client (or myself) even view a place or ask questions.
Long story short, I get your agent's push back, but they're in the wrong here. I'd suggest linking up with an agent who themselves owns property. It's amazing how many realtors own nothing more than the roof over their head. Best of luck with everything, Cal!