I want to break up with my girlfriend because she is overweight

I know the title sounds shallow and it probably is. I don't know how to explain myself. I care about her but I don't find her attractive anymore and I don't see myself wanting to be intimacy with her again. We've been dating for 2 years and on the first year she was a lot more thin and for the last year she gained a lot of weight and I can see it really hurt her self esteem and she's always trying to lose weight and I know it's hard for her. <br>I don't know what to do, I feel so bad because she's been nothing but nice to me, and I feel so shallow to break up with her because of her weight.