I've recently finished my Master's. I'm going to apply to some PhD programs, and I need another recommendation letter. I'm thinking of contacting my ex-advisor in my Master's to ask for a letter. Even though I switched to another advisor after having worked during my first year with my ex-advisor, we got to develop some preliminary research together, and he got to know me reasonably well, I think. He was also my professor in two classes in which I did very well.
Do you think this request is advisable or adequate? If you were in my ex-advisor's shoes, would you hold any resentment against me for switching? The reasons I switched were mostly due to differences in research ideas. He seemed to have accepted the switch on really good terms at the time, but I can't know for certain what he thought of it. I also wouldn't like to lose my contact with him, and I'd like to propose resuming the research with him during the months I will be waiting for the application result.
Edit: I think it's worth mentioning that my ex-advisor and my current advisor don't get along very well. They have some sort of a slight personal quarrel for reasons that I don't know exactly. However It's nothing serious to the point they would cease to say hello when seeing each other in the department, or something like this.