He is definitely not suffering with narcissism. ...His self esteem is low and he doesn't see any good in him self right now.
Believe me, low self-esteem can go with narcissism, and the more you write about your Bf, the more it sounds like they go together for him.
Narcissism is pretty much 'it's all about the narcissist'. Guilt in particular is a red flag - it says he's saying 'Woe is me! Woe is me!'
Remorse is pretty much, 'What can I do to fix this?'
Given what you write, especially given that he's withdrawing from you, it sounds like he's in 'woe is me' mode.
Look, changing from a betrayer to a good partner is not simply a matter of will. It take self-examination and action based on that examination. The introspection part of the work is crazy-making, and I think it's an extremely rare person who can do it by withdrawing and spending time with friends.
Have you spent much time in the Healing Library? (Link's in the yellow box, upper left of SI pages.) Have you read NOT "Just Friends"? Reading in the HL and NJF is likely to be a very good investment for you.