What you say about him seems to fit the criteria for DPD pretty closely. I cannot see any other diagnosis for him that would come close.
I know how much you care for him and would like this to work, but it will be a long haul ahead with not a great chance for complete change. It is up to you.
Here are the official diagnostic criteria for DPD from the psychiatric diagnostic manual DSM-IV:
Diagnostic criteria for 301.6 Dependent Personality Disorder
(DSM IV - TR)
A pervasive and excessive need to be taken care of that leads to submissive and clinging behavior and fears of separation, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:
(1) has difficulty making everyday decisions without an excessive amount of advice and reassurance from others
(2) needs others to assume responsibility for most major areas of his or her life
(3) has difficulty expressing disagreement with others because of fear of loss of support or approval.
Note: Do not include realistic fears of retribution.
(4) has difficulty initiating projects or doing things on his or her own (because of a lack of self-confidence in judgment or abilities rather than a lack of motivation or energy)
(5) goes to excessive lengths to obtain nurturance and support from others, to the point of volunteering to do things that are unpleasant
(6) feels uncomfortable or helpless when alone because of exaggerated fears of being unable to care for himself or herself
(7) urgently seeks another relationship as a source of care and support when a close relationship ends
(8) is unrealistically preoccupied with fears of being left to take care of himself or herself
I wish you great success.