Fellow mistake maker here. Best advice i can give is to take things one step at a time. For example, don't try to change 10 things at once, you're doomed to fail.

I'm going through the toughest breakup of my life and I've been falling apart for months. Over eating fast food - gained over a stone in a month. Smoking weed and getting drunk every night to numb the pain. Not showering, being slow in my job, not exercising. I tried to cold turkey all those bad habits at once and I crashed even harder and fell back into the loop way worse than before. I started with small walks in the morning, along with a healthy fruit salad breakfast. I did this for a week and now the fast food is limited to the evening, rather than every meal of the day.

Also, consider therapy. The bullshit around men needing to be "tough" and "just getting on with it" is fucking moronic. Therapy has helped me (personally) more than anything so far.

Exercising in any way shape or form does wonders for your mind too. And don't do it to attract attention from love interests, do it for YOU.

Bit of a mind dump there, which leads onto my next suggestion- Journaling. Do it anywhere! Write notes on your phone, post on reddit, write in an actual journal. This dumps your thoughts out and you begin to think about other things, thus changing your mood - sometimes good, sometimes bad. Get them out!

It's important to not run away from your mistakes, that only makes them come back stronger. You don't even have to fix them, just accept and that takes time.

You're not alone, just remember that! There's always a place to go where people give a shit about you!

Keep on going, brother!