Unless you're doing things like knocking down little old ladies, stealing suckers from children, teasing cats to distraction or pinching babies way too hard - I doubt you're a jerk (if you ARE doing those things, shame on you).
It could be many things already mentioned - sick of winter syndrome, lack of sunshine, carb deprivation catching up with you, or just plain old loss of motivation because you're well and truly sick and tired of the whole weight loss thing being the number one priority in your life. You've lost 80lbs. in 8 months and, if you're like me, you spent pretty much every waking moment of that 8 months thinking about "THE PLAN". I believe the spirit eventually says, "Enough already - I need a change" and that's what's happening to you right now.
Now, I'm not advocating going wild and quickly undoing all the good you've done - which is something I began to do, resulting in a 20lb. gain and feelings of being a jerk (granted, I was pinching babies at the time.) Soon enough though I started to really, really miss that great feeling I had when in control with my food and exercise and decided to go back to it, but not to let "goal" be such an important factor in my life. Frankly, it was too much pressure and I was at the breaking point. Now I'm on a much more even keel. Fine, I've gone from losing 100lb in just over a year to losing 15lbs in just over a year and I still haven't reached goal after 3 years - but you know what? I'm enjoying having regained the quality of life that was so dimished 3 years ago and while I may not have the all-consuming motivation and desire of the "honeymoon" phase, I think perhaps I'm starting to live like a "normal" person.
Mind you, I'm not going to be an enabler and say "Its okay, hon, you just keep chowing down on those carbs, you can always start fresh tomorrow" - I'm saying "Get a grip, girl! Don't let that 5lb turn into 10lb or 20lb! Change up the mix a little - perhaps back off on the all or nothing mindset and adjust your "if I don't go full max and lose like I did before I'm a jerk" attitude. When the sun comes out try to absorb some of its energy. Most of all, remind yourself that you CAN do it - you've already proved that! Just sit yourself down and sternly tell yourself of all the reasons why you need to keep going!