If they are staying together are they beginning to show aggression towards the other one? Even bonded pairs will lip lock and test each other. If they are over 8 months of age they are old enough to spawn. The fact that they are staying together leans towards possible bonding, the next thing that might happen is the odd angel starts getting harassed. Although if you happened to have a male and two female sometimes you will luck out and the male forms a harem.