I think it's difficult to find love if you have low self esteem, especially if it comes across that way. Some people are good at hiding it, but if your outward persona is low self esteem, sadness and thinking you don't deserve a good relationship, then you won't get one.
Now I don't see that entirely the same as 'being happy in yourself'. I've never ever been 100% happy in myself, mainly due to needing/wanting to loose weight here and there, but I wouldn't ever describe myself as low self esteem or depressive.
Not everyone is beaming and full of confidence, but you should have some aspects of yourself or your life that you are happy about, otherwise it's all doom and gloom which isn't an attractive quality in a partner.
One of my brothers GFs had low self esteem. She would say she's so lucky to have him and he was her prince. Her low self esteem was so evident, that another girl who fancied my brother had the guts to try and muscle in right under her nose, because her lack of confidence almost made her invisible.
When a man catches on to ones low self esteem, he can easily capitalise and take advantage of it. You may be lucky, but generally if you don't like much about yourself and are unhappy with yourself, why would you expect anyone else to think different?