Common dude they are far more than just F-D, at-least this is what i believe. For me their relationship is beyond lust and sex.The Kelly-Andrew IS the story, I would be beyond shocked if after all this they dont find each others arms again, it just might take an update to get there.
With Andy being the Dad, he knows he has to give Kel some space, for her to figure out her own priorities. If that aint being a caring good dad I dont know what is.
Now they are separated you can see Kelly coping with her feelings and she is trying to fill the void but Andrew he isn't even missing her. He is having a fucking vacation with his wife and her partner like he doesn't even care. He isn't even thinking about Kelly.
And now if they decided to come back together then it will feel like forced for Andrew because he seems to be happy with his wife now. It feels like he has moved on.