Hi Kutiyoung, I'm sorry to hear you've been having trouble with this. I'm one of the ones that has had EC for 20+ years (I'm 31) and at my lowest I have felt the same way. My EC is in remission now but due to the nature of the condition it affects everyone differently and even success stories are full of ambiguity because it's difficult to know actually what made the change. There are many that are cured without ever really knowing the reason.
The most important first step is to look at your environment. What is coming into contact with your lips that may be making the problem worse. It might have started from lip biting but it's clearly not being allowed to repair and so you need to look at things like hygiene products that you are using that may be prolonging your chelitis. I would say your best guess is to look at a) your toothpaste and b) your shampoo and soap.
Many products contain SLS. Read here for a success story from someone that cured their lip dryness from changing their toothpaste:
Personally, I disposed of all my shampoo and toothpaste because they both contained harsh abrasives not just SLS. Ideally you want sulphate and paraben free.
Without pictures it is hard to give advice, but if your lips are anything like mine, they start off a ulcerated red and then the outer layers of skin dry out, crack and peel. I would often get tiny bubble blisters which would sometimes be quite large. I noticed that my lips were a lot calmer after the changes.
Say for example, if you are having a shower and washing your hair, the soapy water will run your down face across your lips and down your body, this brief contact may be enough to strip off any skin and re-start the whole healing process. The skin of the lips is only a few cells thick. Likewise, using soap (which will most likely contain SLS or equivalent) to wash your face will by just as damaging.
Anyway, I use an all natural shampoo bar now which can has no harsh chemicals at all just argan oil and coconut oil. And I use this to wash with as well. I suggest you find it online and give it a try, it is made by J.R Liggett's. Pick the scent you want, they have a variety of different ones. For soap I use organic aloe vera. Those liquid hand soap bottles with push down nozzles are full of filth which can irritate sensitive skin.
So, focus on what is coming into contact with your lips first and eliminate these things. Then you can focus on other factors at a later date. Contact irritation is the most obvious place to start. Hope this helps.