Hello and welcome to Healthcare Magic. Thanks for your query.
Since you say that these problems such as short-temper, mood swings and difficulty in handling stress
have been long-standing, it is likely that these may be part of his personality. Some persons can have certain unhealthy personality traits which result in emotional dysregulation.
Your boyfriend also seems to have poor coping skills, which may be the reason for him to get stressed out so easily. There are psychological therapies which can help him gain bette emotional regulation and teach him better coping skils / stress-management abilities. So, you can suggest him to seek professional help.
Wish you all the best.
Dr. Jonas Sundarakumar