You have a boyfriend, not a fiancé or a husband. You have been dating for 24 Sundays or 168 days. Your relationship is very young and you do not have a lifelong commitment. Therefore, you are worrying needlessly.
Besides which, people date for a reason and that is to get to know one another and decide (independently and together) if you have a future together. Now that you are getting to know him, you are learning that he wants to be an officer and has taken the steps to make that happen, as he is in the Cadet Academy. Umm, sweetie, this guy is doing what he says and says what he is doing. You need to wake up and get out of denial that he may very well choose the Police as his career choice, as he IS currently on that path.
You need to wake up and either accept his career choice or leave him if you are going to worry yourself and your relationship to death. You cannot claim "Oh, I did not take him seriously or I did not think he would really do it", because that is exactly what he is doing right now.
Yes, it is wrong your you to stifle his dreams. We all have choices in life and if you do not want to be with a police officer, then go find another man because this man you have has actions that speak louder than words. You cannot cry that you hoped he would change his mind because you know, RIGHT NOW, that he is doing what he said he was going to do....whether you like it or not.
So, you have two choices: accept and support his choices OR leave him now, while you have been dating for just a short time as it will be easier to break away sooner than later.
This is not like a boyfriend who is hiding the fact that he has a child. His career choice is what he is living day to day, so there are no surprises here for you to freak out about in the future, if you should choose to stay with him. THIS is who he is so you either accept it now or move on.
It really is as simple as that.