Your relationship with your husband has changed, this frequently happens with Poly and yet it still manages to shock some couples.
But to be fair (and I hope not crass or vulgar) I really do not think you have given it enough time, it has really only been a week or two (certainly not several weeks) since you said you have given them permission to sleep together but you expected change too soon.
My own thoughts are that you are not really comfortable with this relationship because you feel the threat to your relationship and can't really handle this NRE.
Perhaps Poly simply is not for you? Like many people going into it, especially in a triad, you assumed fully equal level of NRE and was not prepared to be locked out of the NRE.
I also don't believe your threat to get your own bf, I think you said that to shock your husband and get him to feel jealous, the fact that he reacted so strongly is telling, he wants to be the only man but he can't take care of both his partners, he is mono-focused and yet totally willing to dump the girlfriend at a moments notice, it seems like very selfish and unhealthy behaviour all around, if you do continue together please seek counselling and stick to monogamy.