Interviewing for my dream job on Wednesday and I'm honestly confused and nervous

Hope this all makes sense but I just need to vent on this....

I graduated college recently and ended up getting a "salesman-in-training" job at a wine distribution company. It's been alright, the people I work with are great guys, my boss has been awesome, and the job itself has been decent. Sales isn't really my forte but it's enough to get by.

But I applied at another place for my dream job, being a career counselor. My whole life I've been so stuck and confused at what I wanted to do, that even though I may never figure it out I might as well assist others in figuring out their possible careers. I'd also help them practice interviewing and building resumes and such. This company called for me to come in for an interview on Wednesday and I'm so stoked.

But if I get the job, I'd feel bad for my current boss. He's been under a lot of stress at work and has dealt with a lot of shit since he got put into the position a few months ago as district manager. He fired someone and had to cover their sales route while also being a manager. Did I mention he's put in a lot of time into training me to be the next guy to get a sales route?

Here's the kicker, there may be a sales route opening up for me soon (nothing concrete but it could happen). What sucks is I may not be doing it if I can land this new job. Henceforth putting more stress on my boss to start all over again with covering the route, being the manager, and finding my replacement.

I may not even get the new gig, but I strangely feel like I have a good shot. All in all I would just feel terrible for my current boss if I left but ultimately I wanna do what is best for me in the long run.

Also, I applied for the job on Valentine's Day and they called me for an interview this past Friday? Is it normally a good sign that they called and requested an interview so quickly?