I'm currently doing my third postdoc at an Ivy league university. My supervisor is very famous in his area of research and he was very supportive for me during the first year. However, he waited until the end of the first year before offering me an extension so I applied to a few tenure-track positions just in case he wanted me out of the lab. I got two visit campus so I told him about that because I mentionned him as one of the three references. I also reassured him that I will be staying in the lab until the end of my contract (completion of the 2nd year). He said that he is happy for me and that he will gladly write a recommendation letter and support my applications.
Then, his behavior became very strange. For example, he will not communicate with me or answer my emails unless it has something to do with what he needs for some project. He also started excluding from the different projects and the key meetings. Meanwhile, I passed the first campus interview and the chair of the search committee told me in the end of the visit that they didn't receive a letter from my supervisor. So I asked him about that and sent him two remainders so he can send the reference letter. He did not respond to any of my e-mails or messages. So I contacted the search committee and told them that my supervisor is busy. I asked them to change my reference and use my PhD co-supervisor as a reference and they accepted my request. My PhD co-supervisor sent them a strong recommendation letter immedialtey.
A few days ago, I got a verbal offer from the college dean and I'm currently negociating with them the details with her. But I'm still cannot understand what motivated the change in my supervisor's behavior, and wether I should stay in my lab until the end of the my contract or terminate it sooner (I am not sure that it's going to be a nice experience without my supervisor support).