This may just be a polite compliment. Don't be too sensitive. Since you are her girlfriend, you should trust him. You should be able to feel whether he is sincere to you. If you have a good relationship, don't doubt that your boyfriend has affected your relationship. If you have doubts or don't like his contact with his ex-girlfriend, you can generously tell him to delete his ex-girlfriend's WeChat. He will listen to you if he cares about what you like now.