My boyfriend's personality has changed ever since he became a police officer. Should I move on?

My boyfriend and I have been together for 8 years - We are both 26 years old. He's disgustingly loyal, my best friend, and the most amazing man I have ever met… but 4 years ago he became a police officer and it has changed him drastically. He patrols the housing projects in one of the most dangerous areas of NY. The (mostly domestic dispute) jobs that he responds to sound terrible and I try to be understanding. But I'm wondering if he's too uptight for me now. He has a short temper now and I feel like I'm walking on eggshells around him. He's not affectionate anymore. He is always tired and never wants to go anywhere or do anything. He won't hang out with anyone unless they are also a cop. We see each other maybe once a week if I revolve my schedule around his days off (I also work full-time and am in grad school). I've gotten used to all of those changes but now he is studying for the Sergeant's exam and he has no time for me. He’s stressed and grumpy, but apologizes and says it has nothing to do with me. I love him sooo much but I've been dealing with this for years already and if this is what our lives are going to be like forever, should I get out now? The test is not for another 6 months and if he becomes Sergeant (which he says is extremely tough because he is competing against thousands of others), will that make things better? Will I ever be his priority again? I'm getting to the point where I want to get married soon and I don't want to waste any more time if I'm not with the right person.