It is certainly not irrational to feel what you are - however, I would give kudos to your boyfriend, if you haven't already, for being honest as soon as he was. My husband has been poly for 20+ years, and he can still go through a period of being less than upfront when he likes somebody, because he can feel guilty about it.
In your place I would probably ask that he follows your original agreement, and in the future he doesn't introduce people to your friends until you are in agreement to have potential lovers involved more with the rest of your life. Make sure he is really agreeing to this though, and not just saying yes because your request is so reasonable - I've been suffering from a rash of this myself - husband agreeing to all my reasonable requests and then dealing with the aftermath when he does whatever anyway, mainly because he doesn't understand WHY I request something, so he doesn't think to actually stick to our agreements.
This has actually happened a dozen times in the last few months to me, and all of them were miniscule things, but all were broken agreements. It is a fine line between not getting hurt by these things because there was no bad "intent" on the part of our partners, and feeling betrayed. I live in a black and white world and my SO inhabits the gray area. Misunderstandings in relationships are certainly going to come to the forefront whenever new things are happening, trusting the love of your SO is going to help a lot, even when they are acting in a way that doesn't make you feel so great.
I think the best thing is for parties in a relationship to be firm and honest about what they want and need, and to compromise as needed. (Yep it isn't easy at all, my SO feels guilty to ask for what he wants - does your partner have trouble asking for what they want or need? It can be hard to tell sometimes, if they aren't speaking up about things that are bothering them). It sounds like you are probably trying to be clear about these things, and he may be struggling a bit, not knowing what he wants.
I might let him know exactly why you don't want potential partners hanging around until you know what will happen with them, how it makes you feel, if it will make you feel awkward around your friends, what you think would happen if a situation works out, or doesn't, etc etc. If it was just he didn't really understand where you were coming from, so didn't think it was that big of a deal, this might help. Maybe what he really wants is to be able to introduce people he likes to you and his friends to see if they mesh, and wait until he sees how it goes before deciding what he wants to happen - it's his ability to be honest AHEAD of time that sounds like it might be the kicker for you.
If it happens again, or a similar thing with anything else you think you're in agreement on and it turns out not to be the case, you could be in for a rocky road. I've tried making my SO go first in stating what he wants or thinks about a subject before I tell him what I think, because I have gotten too many "sure that sounds good" then he's turned around and done the opposite.
I would also feel hurt by this. I would not decide the relationship was not cut out for poly because of this. I would praise my partner for being honest as soon as you got home, and tell him I appreciate it, but how important it is to me that he thinks and speaks with me before taking action.
Thinking good thoughts for you, it sounds like you have a great head on your shoulders.
Happiness will never come to those who fail to appreciate what they already have.