As it was in the first book, Dark Horse, Out of the Darkness is a menages a trois story that doesn't take lightly the balancing problem these relationship usually have.
Evan and Jeff are an established, and open, couple. I'm not sure I would like them so much if not for the addition of Dan, and this is strange for me since I usually am not very fond of menages. But the interaction between Evan and Jeff had a bit too much the feeling of conventional, meaning that Evan and Jeff seem to be together since they are used to. Jeff has also a paternalistic approach that in a way is good, it is very useful with Dan and his issue in accepting some things of this new relationship, but sometime I found it annoying. On the other hand Evan sometime seemed to much shallow like nothing really matter to him if not his own family: if Dan wanted to be part of that family, good, if not, well in the end he always has Jeff and so he is good.
I think Dan really tried to understand the dynamics among the three of them, and he also realized that something had to be corrected. I had the feeling that Dan is more attracted to Jeff, that in a contest between Jeff and Evan his choice would be for Jeff, but Dan also understands that Jeff without Evan is not an option and so he has to adapt. Moreover, like I said, Dan realizes that both of them, Evan and him, are relying a bit too much on Jeff, and that is an unbalancing factor: they need to lower their dependency on Jeff, and at the same time trying to rebalance what it is between them, Dan and Evan, despite Jeff's presence.
The pacing of the book, like I remember it was in the first one, is quite slow, and there is a lot of overthinking; in a way, even if they find an agreement, until the end there is still the little feeling that things are not yet perfect, that there is room for improvement. This is not only the story of how a menages was born and developed, but it's also the making of a new family: Dan, Jeff and Evan are not the only ones involved, Tatiana, Evan's sister is for sure another element to consider. It's not clearly stated, but I think that she is a cons in the list of Dan to try to make things work, and the fact that she is basically the main character of the prologue and epilogue I think it means something.
Despite more than 300 pages and being this a romance, sex is not really the main course: when there is sex, it's more something in the contest of the story than a recreational activity (both for the ones involved than the reader). Actually I think this is one of the few romance that doesn't end with a sex scene to reconcile all parties involved, and instead it presents a family picture, where for family it's intended the extended concept.