Hi xJx,
maybe your boyfriend is a little bit jealous.You have a new job, described it as being fun, with loads of new people to get to know and maybe he feels that he may get pushed to the side and that you will want to spend more time with them than him.
My best advice to you is to talk to him about it. Sit him down and chat until it is fully resolved, dont let yourselves argue just try to be as calm as possible, if you love each other so much then you will want to talk it through so that he feels secure and vica versa. If your boyfriend isnt going with you for a night out and not seeing you at all that night, he may feel after the job incident that you are trying to pull away from him, maybe he is mentally preparing himself for the worst. Only some suggestions. Hope what ever you try it works and you are both very happy.