Imperative: Missing You - Belinda McBride

In this future world, people are paired (or more) according to an Imperative and it can be two heterosexual people being attracted to the same sex.  So two men find each other and are at first happy but then are discontent because they feel they've been missing something.  Marina was there at the Imperative meeting but felt her partner leave which leads her to a deep depression.  Chance (or more again) brings them back together. Sweet story.  I have the other two in this series which I'm planning on reading.