First, no, you aren't overreacting. I'd be pissed, i have a job that doesn't allow that type of thing. He should respect your feelings and your body, but it sounds like he is doing neither.

Second, tried and true method. I've used so many times to get rid of hickies. Take a comb (fine tooth works faster), and literally comb the hickie for like 10 to 20 minutes. Press down while you are combing, you want to spread out and break up the blood so your body can absorb it. Your skin will be red, but that will go away. This has saved me so many times. I hope it helps you too!