I have been working at an IT company for two years as a co-op. Four months later I received a part-time job as a motion graphic designer. Both jobs gave promise of full-time employment from both jobs. Fast forward two years later my design job has given me an offer I am pretty sure I want to take. My only predicament is the IT company has paid for my clearance process that is on the final stretch. They are also restarting their internship program which they want me to help setup. This offer comes at a really inconvenient time. I don't want to let anyone down but, it seems inevitable. How do I bring this up to my boss and keep things on good terms?
I was in a similar situation before as well. This IT company invested a lot in me. Gave me access to a whole bunch of places, paid for my travels, all that jazz. Not trying to be cocky or anything, but I had a good feeling they wanted me there full time after the internship I was doing for them. Well, after only 5 months I wanted to pursue something I would enjoy a lot more; software development. It was a hard decision for me because I built great relationship with the employees and management at the IT company.
In the end I wrote them an honest letter, expressing my new passion and new direction that I want to go with my career. I mentioned how I enjoyed working for the IT company and enjoyed the people that made up that company. I ended my email with a lot of thanks; thanks for the opportunity, thanks for placing trust in me, etc etc.
My manager emailed me back with congratulations, thanking me for my contribution, and wishing me luck. There were no bitterness. As a matter of fact, I DIDN'T expect any bitterness because I knew of their professionalism. If I were expecting bitterness then I wouldn't have had a hell of a time making the decision to switch careers.
So in the end, just be honest. They should be professional and understanding of your choices. If they aren't, well then aren't you glad you didn't stick around longer?