I spent a reasonable amount of time in therapy discussing my sexual side, so I know what it's about and where it comes from.
For me, sex was the only part of my life that my mother didn't have access to, to monitor, make judgements about, and pass comment on. It became important because it was the only part of my life that allowed me to be myself and with that feelings of escape and freedom - and when things were particularly tough at home, that's what I did. I was quite careful, and usually selected a target that I already knew and who I knew would treat me relatively well.
But it wasn't just the freedom, it was also about being good at something, as I was never good enough at anything in my mother's eyes no matter how hard I tried, and this allowed me to not only be myself and be free, but also to do something right and be good at something in life.
I did have issues with the morality of it all, as that was something that was very much preached at home - no sex before marriage, and women aren't supposed to enjoy sex they just do it to keep their husbands happy ...and this did become integrated into my sexual preferences, to be "punished" gave me permission to both do it and enjoy it.
I don't need to act out anymore, I know if I ask myself what it is I'm feeling inadequate about, that is making me need to escape to a place where I will feel useful and good enough - that as soon as I acknowledge that it's about inadequacy and start to address the driver, my desire for sex will diminish almost instantly.
If only the eating was this straightforward!
It's not though, the eating is very enshrouded in a double bind type relationship - where I'm damned if I do, and damned if I don't. I realise my mother had/still has issues with food, weight and body image. Her issues turned her into "a feeder", she fed me all the things she wished she could eat herself, and no food must be left where it might tempt her - you couldn't save anything for later, and open packets always had to be finished off in the same sitting. If we had a cake or anything like that, she would force 2nd and 3rd helpings upon us until it was gone - and she would get angry and fly into a rage if you tried to refuse anything. Yet she judged us on our size and weight, in the same harsh way that she judged herself too. You couldn't win! I just wanted to be "good enough" and feel loved by her - I ate whatever she "forced" me to eat regardless of my body sensations - the feeling full or feeling sick - it was more important to be loved, and I crash dieted when she forced me to (that was more literal force, because she withheld food), because I didn't like hearing her say she was embarrassed and ashamed of me, and that I was a disappointment, so again I learnt to ignore those body sensations associated with starving, because I just wanted to be loved. In fact I actually learned to view the discomfort of the body sensations associated with bingeing and starving (which is what it was), as positive things, because I believed they'd make me "good enough" and then she'd love me.
(I see here, the similarities with the pressures you felt Joanna, to eat lots yet still be thin, in fact my mother did such a good job of telling us how wrong bulimic purges were and how we must never ever do it, that in hindsight I wonder if maybe she sometimes did it herself.)