A sudden change in personality can indicate anything from an STD to MI issues. He never mentioned feeling like this before?

I think the physical indications of his poor health say a lot about the state he's in, unfortunately if he's a grown man no one can make him go and get the help he needs. If there was something medical behind him leaving you I would wager it needs treatment pretty quickly. His reaction to you was nothing short of extreme.

I would speak to his mother, and explain that he needs to get help before you're willing to have anything to do with him again - after all you wouldn't want to go through this sort of thing again would you?

It might shock him into realizing that he needs to be responsible before he loses the life he built with you forever.

For now I would concentrate on both yourself and your son. Its Christmas soon but it doesn't have to be miserable, after all you have each other so you're not completely alone. If there is no family you can stay with there are usually women's shelters who could advise you or temporary housing if you contact the local council. Having a young son should definitely aid you in finding somewhere quite quickly.

I'm somewhat surprised his mother wasn't willing to put you up for a short time - did you have a difficult relationship?

I hope things work out for you - it must be very shocking but you know where your priorities lie you've just got to move forward. Eventually the pain will ease. Good luck.