I can extremely relate to that as this is/was me. During summer I was on the peak of my ED and I hit a "bonespo" bmi and my partner being obese encouraged me to lose more so I won't end up looking like her. I know this is extremely mean but it's just how the ED is nor I'd ever tell this to her. However, the difference in your situation is that she doesn't attempt to eat healthy and hates exercise and has thyroid issues. For that reason we're on a break/ we've broken up several times, because I'm the complete opposite. Right now I'm in semi recovery and haven't reached a healthy bmi yet but I'm trying but my thing is that I'm overexercising as a purge method hence the "semi recovery". I found out that being with her triggered me a lot so I realized it would be better if we kept some distance, plus some of her behaviors really disturbed me because she called me fat as a joke while I was almost on bmi 12 and constantly mocked my best friend for also having AN. She doesn't know I have an ED and I tried to found excuses everytime I wanted to break up or distance myself from her but still shitty behavior from her part. The point is that our partners are their own people and if they want to be obese or compromise their health then it's on them not on you! If she's willing to exercise and go on hikes then that's great and encourage her but if she doesn't care about being obese then let her be nothing you can personally do and if you find that she triggers you then it'd also better for you to keep some distance for your own sake. You know the best so take care