My boyfriend wants an open relationship and I'm not too keen on the idea
Open relationship?  Why did he say so? 
He just said he likes the idea of polyamory.
Wow,  so,  are you going to allow that?  Can you share your man? 
I don't think I can, I feel like it would be an act of infidelity based on my expectations of the relationship
Cool.  So what do you intend  doing.  If it's me,  I will take a walk 
I'm thinking the same. He seems to think it's ok since the concept of an open relationship has been recognized since the 1970s.