Because of past conflicts, I don't believe my advisor will write me a good LOR for postdoc positions. What should I do? How essential is having my advisor's letter for post doc application? 

I had a pretty bad relationship with my advisor for more than 4 years since I joined his lab and sometimes the relationship feels like slow inflammation that can easily flare up. We had very different opinion on how I want to approach my thesis and we argue very often on the experimental approach and the angle of attack. After that, he turned passive aggressive and completely hands-off. I noticed that he started slow to response to my email and given me very small amount time for meeting in comparison to other people in the lab. However, I proved to him that my approach was right and wrote the full paper myself and got published. 

Recently, I got contact by a post doc employer who interested in my own work and request letter of recommendation. I asked my advisor for letter and he told me that I should write my own from which he can modify. I feel this is quite strange as he had wrote for all the other people in the lab, including a departing post doc who is currently interviewing for job. He told me he had done the same for other people but obviously he lied to me. 

I further asked if he can provide me a copy of a completed version of the recommendation but he refused. 

My question is should I still trust him to write my letter and is it essential? This post doc position is a great opportunity for me and either way I do is a big gamble.

Update: I decided to let my advisor wrote a letter for me and I think I may have made a big mistake. Since he wrote my letter, I asked the post doc lab head if my letter is completed and I no longer be able to hear back from him. Before that, he was quick to response to my email and showed great enthusiasm. As an insurance, I use one opportunity I have less desire to as bait to test the water and I still have one more shot at another position I really want.  Now, I'm thinking requesting open letter from advisor from now on for any future position or use letter service to check the letter. 

Any suggestion? Thanks.

update: Great news! Got interviewed and offered at top ones! Thanks everyone!
Once it became clear that you were not going to follow your advisor's advice on important issues, it might have been better to switch advisors to one you could work with. Instead, you continued, in effect, without an advisor. The limited meeting time, slow e-mail response, and requiring you to draft the LOR all suggest to me an attitude of "Why waste my time giving advice that won't be taken anyway?".

You cannot be sure he is lying about having other people draft their own LOR unless you have talked with every person for whom he has ever sent one. He may feel he knows some students well enough to write an LOR from scratch, but needs a draft for others.

The best you can do at this point is to write what you consider to be a reasonable LOR and give it to your non-advisor.