I’m currently a web development intern in a small-sized company. My internship contract ends this Friday. Two months ago a superior told me there would be a possibility for me to be hired permanently in the company. I told him I was still unsure whether I wanted to enroll in university for a master program next September, but that I would of course wait for their offer and take it into consideration. Flash forward to last week, they finally presented me an offer.
I have thought about it and decided not to accept it, in order to enroll in university next September, and be able to get some rest this summer (I’ve been an intern since late 2018, and I got my Bachelor’s degree in March 2019, so I’ve been full-time working while taking my last exams and writing my thesis - it’s been quite stressful, and I haven’t had time to properly recover both physically and mentally).
Today I communicated my decision to my boss, and he tried to make me feel bad for not telling him beforehand. He basically took for granted that I would accept their offer and keep working for them. He wants me to keep working until mid-August in order for him to find another person to take my place, and not to fall behind on work when he leaves for his vacation this summer.
Tomorrow I will tell him I have no intention of keeping working after my contract ends. Even though I know I’m not in the wrong, they managed me to feel somehow guilty. I didn’t need to give notice legally, since my contract is ending, and I never told them I would for sure remain in the company.
I feel one of my biggest insecurities is the fact I lack assertiveness. I am really anxious about communicating these things tomorrow. How can I do that in a firm yet polite way? Besides, I’m really worried this fact would make my boss give bad reference for me when I apply for future jobs. I've never had any problems with my boss in the previous months.