Probably closer to a 4.5. 

When I first started reading this book, I honestly didn't expect to fall completely in love with all three of the characters. They were distinct and well fleshed out and literal perfection. I honestly think this is a book that got better as it went on. It even had me a little misty eyed at certain parts (especially as someone who entered the poly scene not long ago). 

I do think the world building could have been fleshed out a bit more, but (given that the ending seems to be setting us up for a sequel) I'm really hoping we see more of that in the sequel. 

This will be a book that I recommend and tell people about every chance I get because it was so good.