Should i change jobs?

I have a job that I love. Its challenging and fast paced. I work for doctors that I admire and respect. And for the most part every1 gets along great. I do however get more work dumped on me than anyone else. If I get behind no one helps me, despite the fact that I help anyone out whenever they need it. I was told I would get a raise after 90 days that I did not get (I've been there 8 months). And when its a bad day its a really bad day. I was almost laid off last month and after surviving the first round of lay offs and absorbing job duties was told that I may still be let go in a few months. The dilema is that I still love this job. But I have an opportunity to do something new. Take a job with great benefits, working with children which I love and really have a knack for, and its one of those jobs that you don't get the chance at often. Its a job you could stay at until you retire. I got the job. Im so excited, but so uncertain about leaving the job I have now. What do I do?