This wasn't really one book, but more like a series of shorts. Each short had its own arc, and together they show the relationship of Chris and Matt, starting with how they first met and ending about three years later. It is, as the title suggestion, the evolution of love. It was very sweet.
Since this isn't one cohesive book, there is no real plot or conflict. It's more like real life; you get little windows into pieces of their life together. Some of the stories have real conflict in them and some don't really. But you come away with the overall feeling of the deep love they share for each other. It's a SUPER romantic, gushy love story and if that's what you're looking for, you'll be very satisfied.
The only real problem is that of course, each short has sex in it. Which if you're reading it the way I assume it was originally intended - in bits and pieces - would be perfect, but reading it all at once it did get a little porny after awhile. There was just so much sex, I started to wonder "aren't these guys tired yet??" And there were a couple scenes that made me wonder how much gay porn Ally had to watch to research this book. (A real trial, I'm sure...) That and the fact that it was so over-the-top saccharine are why the 4 stars instead of 5.