Not much one for conspiracy theories but the Express article refers to an affair:
The tribunal heard that married Benning was suffering from depression after having an affair with another member of BA cabin crew who became pregnant but lost the baby.
Claims that she complained of harassment by Benning were denied by his legal team.
Express.co.uk - Home of the Daily and Sunday Express | Printer
There have been reports about 'trouble' within BASSA related to the fidelity of some crew. May be rubbish but it's a rumour network. Was Benning dumped for his indiscretion?