I wouldn't tell him you like him but I would tell him your poly. If he is a fairly intelligent guy he already knows you like him and might be hanging on to this LDR because its an excuse not to ruin your marriage by doing something with you. Bringing up the fact that you like him may give him hope and end his other relationship prematurely, though, and you don't want to cause that. It never ends well.
"Regret for the things we did can be tempered by time; it is the regret for the things we did not do that is inconsolable." - Sydney Smith
Kyle: 27 year old male
Katie (rymmare): 25 year old female
Kids: girl: 5 years old, boy: 3 years old