Dear Mr. Medela,
I am writing to [not so regretfully] inform you that after a combined total of two and a half years of seasonal employment, your services are no longer needed in this establishment.
Although you have not always been on the friendliest of terms with your coworkers, you have proved yourself very reliable and always a hard worker.
I wish you only the best in the future, wherever it may take you [but preferably not ever at this place of employment...ever]. Should you need it, I would be more than willing to write a glowing recommendation for you or any of your relatives.