TL;DR
I work on many projects at the same time, but my boss feels that since I don't meet the deadlines on the main one, I'm not committed. I am probably more committed to the company than others, but since I have more projects in my bag to care about, the main one goes at a slower pace.
My boss will only look at specific results, not at global progress. Focusing just on the main project means causing problems to the clients and the rest of the employees.
How can I convince my boss that my commitment is real, or understand his idea of commitment?
Background
I had a meeting where my manager and the boss told me I am not committed to my project. The thing is that after 5 months working there I was switched to another role. Even then, I still had enough knowledge to work on both sides, so from time to time I had tasks from my previous role as well. This, along with other projects that have appeared over the time (colleagues going on holidays and I taking that one, "projects-that-look-pretty-much-like-what-you-did-in-your-last-job-so-it-should-be-easy-for-you", abandoned old projects from previous employees), has been my everyday for more than 3 years. My project, though, is just one, if we consider what my contact card says.
Anyway, my manager knows I'm in many different projects. He's actually pleased because I have a cross knowledge of many parts of the company. My boss also knows I do different stuff, but to him, it only represents 5% of my every day (despite the largest bulk of tasks come from him). I'd say it is not 5%, but rather 60%.
This causes my project milestones to be less on time than others, while I achieve many small tasks that anyway help solving errors or help others finish their projects.
My boss and my manager base their assumptions on the work logs we present monthly. Since my main project takes longer to finish in favor of other stuff, it looks like I'm less committed than the rest, and I should pay more attention to my projects. I have, for a week, played the "This is not my problem" card to any person that came with problems, but to me, this is actually less committed than anything else.
I've done migrations at home on my own from 2am to 6am (to avoid users being disturbed), coming the next day at 9:30am to work. I've come on Saturday when everything was messed up by an upper decision. I've postponed my holidays to finish a project my boss considered "it should be already out". Even this meeting forced me to deal with a train delay of 3 hours (where my manager was already warned and I had the permission to leave early). Yet this means no commitment to the boss. Enough to say, I'm the only one doing these kind of things.
How could I put in my boss' perspective of commitment, when I already feel committed?