Thank you very much for the advice.
I did talk about it with boyfriend and he's not opposed to the idea, but he is also a bit perplexed on how it'd work in real life. We don't know anyone in a poly relationship and we live in rural and old-fashioned country, so it kind of feels like something out of a movie to him.
Boyfriend in potentia is a very kind and accepting person, but he comes from a very narrow-minded family, hence my reticence in telling him. It's not only awkwardness, I know it would come as a shock to him that this kind of relationship even exists. That doesn't mean that he would reject the idea right away, but I am sure it would take some time for him to fully accept it.