It is very playboy for a boyfriend to chat with his female colleagues after work. Because he already has a girlfriend, he should treat you wholeheartedly. He should invite you to dinner or accompany you after work, instead of chatting with female colleagues immediately after work. If your boyfriend does this for a long time, it won't give you the sense of security and happiness you want. So it's normal for boyfriends to talk to female colleagues after work. If it is nothing occasionally, it is normal for him to be like this for a long time.