Is it ok to let SPITE drive me to lose weight?!

I'm really frustrated right now because after losing a ton of weight, I've gained about 8 lbs back over the past 10 mos.  Not a huge deal. I can lose it again and I will but here's why I'm so upset- when I was at my thinnest, my sister-in-law (who had just begun to lose weight) asked me what size I was. I didn't really think much of it but it was obvious that she was comparing herself to me.

Anyhow, cut to Thanksgiving Day and me 8 pounds heavier. She has continued to lose weight. She asks me again what size I am with the obvious hope that I will ask her. I tell her my size. When it was obvious to her that I wasn't going to ask her what size she is, she offers it up! (Of course!) It's so obvious to me that she really just wanted me to know that she wears a smaller size than me now. Not only that but she says that women sizes "fall off of her" now and she has to buy junior sizes.  That's right after I told her my size in "women's sizes." What a &%#@#!

I don't get why she has to make it into a competition with me! It's so annoying! But, since she started it, I'm now motivated to blow her away. I will see her at Christmas but then won't see her again until March. My goal is to be in her size (or smaller) by then. 

So, my question is- is it ok to let my anger at her drive me to lose the weight?

Hey,

I did a quick look at your profile and noticed we have a lot in common! I see your interest is cake decorating, and I was a lead decorator in Chicago for the past year and a half before I decided to go back to training (random, i know lol), and I get heart palpatations too, AND I can identify with the orthostatic hypotension low blood pressure thing. It was just interesting to see the titles of your past posts; they coulda been mine lol!

Anyway, the problem with using spite as a motivation is it can backfire. negative emotions are like that. And not even negative emotions, but any emotions that are not centered on yourself when you're dealing with the very VERY personal and vulnerable journey of self betterment can be dangerous and backfire later.

I've dealt with people like that before, and what's funny is their weight loss when they were using me as competition never lasted. It worked in the short term, and made me feel weird, but ten years later guess who still weighs a healthy weight? Me!

Part of health is developing a sense of self and being a little unshaken in that. We are social beings, but at the same time part of our whole journey here with our bodies is to come to peace with them.

Good luck!