Here is the situation. I was Working on a sales job about 5 months ago and I landed a huge client for our company and so we received a big contract from them. I approached my boss about a raise because of this contract and because I had another job offer (and based on past performance) and I received a significant raise in my salary. Today, I have received a job offer from a company that pays 15% more, better benefits, new environment, new experiences, etc, and I am excited about it. However, I also really like my current job. The manager made it known that my first raise came with some strings. One of which was my next raise won't be for 12 months. I didn't think this was all that fair but I understood. This was not in any contract but verbal.
And so I am stuck on how to approach my boss about this. I am not asking what I should do. I already know I am going to approach him and let it him know that I have another offer. I am unsure how to put this across. He made it known I would not get another raise for 12 months when I received my first raise, but I think it is wise to at least bring it up to him.
Some clarity: If my current company matched the job offer, I would stay. If they came close to it, I would stay. If they don't move at all and are firm on the 12 month deadline, I'll leave.
My question: How do I bring this up to my employer in the best way without burning bridges? I'm afraid that even if he does match it, he won't trust me because I could be seen as constantly looking to leave. And second, he might see this as me using leverage for a second time to get a higher salary.
EDIT: The big contract is the one I currently work on everyday. Unfortunately if I left, they would not renew (im the only one at our company who knows their finances left and right). I wish this was not the case but it is. My employer knows this as well, which makes it feel like blackmail. Yes I could train someone in the financial aspect, but this is a large client with relationships I have developed and they would easily move on to someone else.