But unfortunately, I don't have any sMerit to send. The last merit I had received (as you mentioned), was decayed or expired or gone before I log back in in Bitcointalk. I didn't get to spent it. This happened to me before as well. I have received 11 merits so far and I didn't get to send any merits. That is why I'm interested to know how long I can have spendable merits?
First thing, sMerit decay has not be introduced to the Merit system yet. What we know is that theymos had said about introducing one in future but that has not happened yet. So your sMerits could not have decayed.
11 received merits would give you a full 5.5 sMerit to spend of which 5 are immediately spendable.You must have sent them at some point - probably 120days before which is the reason why we are not able to see them anymore.