I don't think he has anything to apologize about; he's a very honourable man. It's not his fault the majority of the country has been brainwashed to reject socialism and chooses to follow dog eat dog sentiments. The majority of people probably didn't look at his Manifesto in depth and chose to reject it out of hand like sheep out of ignorance.
Whatever one says about Corbyn, and I appreciate we unfortunately live in a society riddled with right wing values so he was something of a mismatch, the man has great integrity and towers above nearly anyone else in Parliament.