Mid-20s, yet emotionally incapable of healthy loving attachment, s*x or consistently taking care of myself. What's wrong with me?

Basically, whenever I start to like someone I become weird enough that I don't know how to act properly. I also become very unhealthy mentally. I'm not sure how to attach to people in a healthy manner in general.

Casual sex just seems incompatible with me the way it's done in this society. Basically I'd be happiest having a fwb until I find something short of a soulmate (I know that doesn't really exist, but someone I can feel that way about). The issue is I don't know how to put limits on my own emotions and depending on a day I'll want a serious relationship or a quick f*ck with that person, before I'm even close enough to make any kind of moves. I haven't actually had a fwb ever, but I would like to try. I think some girls have wanted that with me but I wouldn't see them often enough, and ultimately I mess up.

I want to work on myself but whenever I tried seriously I either burnout mentally or get sick (from a burnout physically). Lately I decided to try an extreme weight loss, and despite rarely keeping below the desired calorie limit I managed to probably keep a serious deficit on most days. Now I got sick from cold/sore throat/whatev and I don't keep track of calories as much. Probably from starving, although I wasn't really hungry anyways.

I'm a man btw, interested in women. I know I'm short, and a little overweight (enough that my body seems to repulse some other men, but never got comments from girls), but it doesn't seem to be too much of an issue. I feel like it's something in my personality and emotional regulation but I can't put a finger on it. My behavior makes sense to me, mostly.

What is wrong with me? How can so many people around me date, train, improve their lifestyles, explore their interests, goals and sexuality while I just spin in circles, just slowly progressing in my career and not having a life besides it? Am I just so slow at maturing???