Whenever you are at work or looking for a job, you look for a solution, not a problem.
Your solution:get a job and don't burn the bridge.
If I were you , I would tell your current boss that you appreciate his offer and are willing to work for him in the future, but since you have accepted the offfer from another company, you might just have to leave this company.In this situation, if you don't like your new company, you might be able to come back.
