I solved this a while ago (for myself). If it works the same for you, you are trying the wrong thing.
As NJs we are very future oriented. We plan. We expect. We dream. Introverts even more so. We do it so we don't encounter something unexpectedly. We want to be (emotionally) prepared.
So don't try to not expect anything. It's not bad to form expectations.
Instead imagine, plan, dream and expect more than ever. The solution is in HunterO's post.
Don't stop developing expectations. But stop developing solely the expectation of the worst. ALSO imagine the very best!
Encounter a new experience? Imagine the very worst and the very best that could happen. Prepare emotionally for both cases. At first I preferred being prepared for every possible future, but that's impossible. Expecting both the worst AND the best will mean you got both extremes covered. No surprises. It's about balance
Step 2
If you succesfully do this, you might get confused about what to really expect. But it's a step in the right direction (it was for me). You created two extremely different expectations, that can't both be true. This difference didn't work well in my mind. I didn't know what expect. I didn't know what was true. Horrible.
The next step (2) is accepting that you simply don't know what to expect and that you don't know what is true. For now. Going into the future will reveal these things. It is your goal to go out and test your expectations. Best scenario: He loves me like no other. Worst scenario: He's been disgusted with me all the time. What's the answer? Go forth and test it by confronting your ENTP!
Step 3
Next issue that arised to me (just writing it all out as it might be helpful) was that I couldn't yet test what scenario was true. I was stuck in limbo. Impatient to find the truth. I had to prevent myself from being rash and too quick. Just texting her wouldn't really work. I was seeing her next week anyway so I had to wait. This waiting sucks...
Step 3! Accept the unknown. Even embrace it if you can. (I just threw these words in google and got a lot of how-to's, steps and guides explaining this.) I've been able to do this sporadically, but I'm still impatient sometimes. I'm not afraid for a bad scenario, because I prepared for the worst. I still want to confront it, because I know how nice a good scenario will be.
But so far the first step is the most beneficial to me. Both expecting the best and the worst will never bring me into an unexpected situation. Except that one time something happened that had never occured to me in my worst nightmares... But, hey. Sometimes life is hard.
PS. Best about this is that it jusfities me imagining me and a girl together 30 years from now with children. I'll also imagine how she actually hates me. In the end it's likely somewhere in between *shrug*. But you never know!