Its frustration when a supposedly easy fish doesn't do the deed.
I have found that they require a tight cave, for the first time I saw my BN at it, the male has to trap the female in the cave, so a good tight entrance makes it easier.
As for trying to feed the males when they are nesting I wouldn't bother, They will eat when they are ready, just make sure the male gets a break between batches and he will be fine.