the big mistake most men make, even those who play protector in the beginning, is that over time they slowly, every so slowly, start to interact with their gf/wife as they would their mother. they slowly start to burder her with their inner thoughts, with the stresses of their life, etc. - they start to show her more nad more how 'human' they are (ie. weak).
and while a woman will be responsive to this short term (because it makes her feel that she is developing a bond with you), if she sees to much she starts to get buyers remorse - she starts to think 'oh man. I never thought he was this weak. what's he going to be like in 10 years? i better get out of this now."
like i say, general rule of thumb, turn to anyone BUT your woman for support. i mean, go see a psychologist once a week, go for beers with the guys, anyone BUT your woman.