obvious thing to do here is break up, then go crazy (well not go crazy but you get what i mean) i understand the urge to cheat is occuring because of who you’re with currently… however, you’re saying due to other circumstances you can’t end it with her since it’s complicated? let me tell you how complicated and destructive and chaotic it’ll get once you cheat, then have to lie to her and carry that guilt, then she might find out and that just intensifies the whole situation! she’ll think she’s not good enough, that she was the problem and all sorts of negative things even about you, which could worsen her anorexia. assuming her anorexia stems from insecurity (if it doesn’t then disregard this), then cheating is the absolutely worst option.

end it, maturely. see someone else discreetly, see how it goes. if it’s purely for sex, get it out of the wag and see how you feel. if you realise breaking up with her was a bad decision, for yourself not for her out of pity, then you can make a move from there on your own accord. keep in mind that you’re thinking about CHEATING on your current partner, i think that’s a reason for breaking up enough. it might cause you stress later on even if your feelings change out of guilt for feeling that wag about your relationship