if i remember it correctly, this is their agreement from the very first time—including both fams. they need to have seggs to avoid the curse. once they had one, then it's done. that's why momoki was worried if chikage will leave him after they had seggs. cmiiw
afte they did it for the first the seme just left... and is gone for awhile without letting the uke know ahead of time.... WHY?