I have been there man don't give up. Seriously our happiness as people remains equal. I don't know what got to where you are at. Whether it was escapism, a lack of awareness, genetics, or simply nihilistic glee. You probably are a really smart dude and so the apparent futility of somethings may not appeal as much to your filters as it does to others. Personally I hate vanity, but I began my fitness routine and found happiness for the action in and of itself. Presently I have kept the weight off for few years now. I am by no means an expert, and still have rough days.
I would start by getting the Power of Habit. It is also an audio book. If you like audio books they are great for biking or walking. The best advice this one has is insights into the nature of triggers, cues and rewards. Know thyself and make your bed. Learn about the awesome bad ass baby monkey or astral explorer you are.
Find your Tao/calling. Find that one fitness activity you can do first thing when you wake up and do not give your inner dialogue time to kick in. Answer it when it's tough, easy and see how the appreciation unlocks with the awareness of simple small measurable accomplishments. Appreciate the slightly new that is always there. Read more if you dont believe me. Personally I love Yoga. It relaxes me which stops the emotional eating and it shows there are no fuck ups. There is no Yoga pose fuck up. Yoga is about the discovery of the release of obsession and ego. Most people live their whole lives either obessesional hiding insecurity or egotisticaly avoiding it.
Meditate! I don't know the root cause of self harm and I still have some. Maybe there isnt an origin and Western society needs to come to terms with allowing unfolding. Don't accept other people's judgement. Most people don't even care and we ourselves are overly self critical. Learn gentleness with yourself. You are a gorgeous, graceful story-world whose desires and beliefs are just as important and valid as anyone elses. Take 30 mins to calm your inner voice if you can. Learn to respect your own relative completeness and leave absolute consistency to Nature.
Use the TV in conjunction with your exercise equipment or turn it off. Too much in modern society TV is God. We seek amusement as living adventures indirectly when truely the source of our happiness is our own mind. Mind to your mind.
I believe you already are the best version of yourself. You are striving to improve, which makes it so. So long as you can hold onto that mentality of not running away from your problems you are doing it. The external world takes time to change as our reality tunnels seek to frame optimal mindsets for all things. The ideal maybe a fantasy, and yet it is deceptive to say we are not already some inseparable part of it. Take time's flow as a validation of this. Truth and meaning are emergent sometimes from adhoc rationalizations of right action and word. See the right mind that appears as an ever present illusion. Enjoy the journey.