There's definitely a line where Extraverted Feeling (valuing the social harmony over individual needs) can turn into a mental/emotional issue like codependency and lack of boundaries. Not all Fe users are codependent, and not all codependents are Fe users. One of my friends is an ESFP, and unhealthy Fi can be just as bad, believe it or not. Her codependency might not come from the same source that a Fe-user's does, but it has the same result in poor boundaries.
For INFJs, one of the best ways for us to work through a problem is to fully understand the scope of it first. We need to get the big Ni picture of how it all fits together before we can break that down into bite-sized, actionable items. Also, use the very function that's making this a problem in the first place. Externalize your thoughts and feelings about your struggle with this. Write down your frustrations, talk to a professional or an understanding friend. Get this out of your head and out in the open where you can look at it and handle it. Asking for advice here is already a great step!
For myself, I just went to my local library and read up on it. This one was helpful for me, but there are many more just like it, plus online resources. You can also do google searches for articles that come with worksheets and stuff too, like this: https://positivepsychologyprogram.com/great-self-care-setting-healthy-boundaries/#what-healthy-boundaries
It's important to remember that having Fe doesn't mean you're never going to be able to put yourself first or learn to value yourself. It just means it's going to be a harder lesson to learn than others. The point is practice. Do the work, apply the knowledge, start building results. With time things will get better, but you need to learn the power of No, and that it's ok to not be everything to all people. You're important too, and how can you help others if you don't even feel like you have control over your own life?
> I think OP's going to ditch this girl[...]
Nice projection. Nice to see you in good shape.
> Human will power is OK for some things. But it has its limits. And sometimes the desire for something grows in strength until its stronger than the person's will power.
This reminds me when I started extramarital sex after 8 years of my past marriage and it was just great. Consequences were shitty and could be way worse, but it fits your description - I fixed something that grew in me for months.
Also, my "problems with dieting" during past 5 years were actually life-saving instincts. When I got myself down to 78 kgs for the first time I was actually severely malnutritioned. For the second time - also malnutrition, but lighter. I thought I had "yoyo effect" and that I "compulsively overate" but no, when I was severely malnutritioned because of me and my eating habits, so what kicked in was not overeating - it was actually life-saving instincts. Now I am on my own dieting system that I came up with few months ago, nothing special but it is something what WORKS for me, I keep muscle mass, BF is going down. My basic plan for that system of mine was just like you described - "permanent and healthy solution for my eating until the end of my life". And bam, there it is. So I guess you're right if we talk about food.
If we talk about human relationships and codependency in particular, I'm too fresh to realize what I used codependency for. I don't know yet what I have been trying to escape. Hell, I might never know, I'm reading this "Codependency for dummies" book and I feel like I could go psychotic any time, this is so big amount of knowledge at once that I can feel literally my brain re-wiring, after a few pages I go take a quick nap or just play with my computer to let some stuff sink in, to take my time to read it. Matrix analogy or not... I'm not Neo, this kung-fu learning is going way too fast, but I can slow down, I can put the book down and just meditate on it. The good thing is, that I stopped connecting all my obsession with a particular person, namely ex-wife. I have flashbacks from my life and from Bible, I understand more and more of it. And it is not a pleasant feeling actually, but it's not a pain. Bitter taste of the red pill maybe.
And this is what OP could accomplish easily. But that's not the deal. My parents raised me the best way they could, I can speak English, I can program computers, I can perform anesthesia, my IQ is flawless, I have good genes, I lift 2 plates on deadlift. My father was an alcoholic and my mother was an adult child of an alcoholic and a codependent. I feel that she was a lovely mother for me and used me for company and/or protection when dad was "in a bad mood", but immediately ran to my dad to "get her fix" when he became open towards her. This perhaps made me mad, I saw how much suffering is she going through and I wanted to save her, but in my child's mind I had no idea that she really does not want to be saved. I bought into this schema and implemented it in my adult life. It ended... it actually did not end yet, but after many years of suffering I finally found the solution that works. I believe that the same thing happens to my boys when I leave them with their mother, but that's nothing I can control, so - whatever.
As for OP, I doubt he will read the above paragraph. He is focused on other things. This is also a characteristic trait of codependency and other addictions. He can not be saved, he does not want to be saved. He's just acting like it, so he can victimize himself more and more, then he will do some magic tricks and his whore will get back to him, fixing his ego even more - that's why he needs the victimizing part. Or, he will commit suicide or some other visible act of sick ego. But you know what? In the end of the day, as u/whinemoreplease says, it does not affect me at all. I could not care less.
Take good care and thank you.
EDIT: I actually upvoted OP's post, because I think our comments are very valuable and high quality material. I find myself coming back to MRP for the comments more and more, I don't even read those posts sometimes, just the comments...