It also leads to some grandiosity and feeling too responsible to other people. This is a condition called co-dependency. A further danger arises because we often then treat our later relationships in the same manner. It is probable that you would take care of your friends or love relationships a little too much as well. As I said, it doesn't surprise me at all that you are depressed.
Depression often runs in the family via genetics.
You also said you get depressed for around 3 month periods. This might also be important in making a good diagnosis. It might denote bi-polar disorder or some other type of cyclical mood disorder. I would certainly recommend that ongoing counseling would be helpful and a good psychiatric workup would make sense to evaluate whether you do need medication. If it were possible I would suggest family therapy because although you are depressed you sound healthier than them.