Root cause

I just finished reading Bob Greene's blog on Larry King Live on the root cause of weight gain and that got me thinking. I have never really explored why I gained so much weight in such a short space of time? My dad suggested that I got too happy and comfortable in my relationship with "my bf". My bf on the other hand believed that my sedentary job and then studies caused the problem.

Can these be the reasons for my weight gain? I don't feel unduly happy and/ or comfortable and I have been sedentary before without gaining weight. I know have been a bit depressed for a few years and unsure of the direction I want to take my life but.....