Am I a jerk for not telling my boss I may be leaving?

I have been actively looking for a new job for the past few months. There’s nothing “wrong” with my current one, it was just meant to be temporary for me. A resume/experience builder if you will. Now I’m looking to move my career forward. But, for fear of telling my boss I’m looking for a new job and waking up the next day without any job, I’ve not told him.

My plan has been that I would wait until I had secured a new job and then give him the usual two weeks notice. I’m not looking forward to that day. In fact I’ve not told any of my coworkers that my g/f dumped me about a month ago, so that I could use the excuse of moving closer to her for our relationship when explaining myself (rather than just… “well hey, I don’t want to do this anymore…”). That of course has caused some other awkwardness as I had no explanation for my depression the last few weeks, and I had to make up some “stories” of things she and I did… but thats another story, ANYWAYS…

Am I a jerk for not telling my boss? Not that he won’t be able to find a replacement, or that an additional few weeks would really have helped in training… but yah? How would you have handled it? And a side question, how would you start that conversation with your boss?