Suppose you make a compromise and you can be bold together. If your girlfriend has a self-aware name, try to be less close to other boys and take care of your feelings, because you already know it.
Your girlfriend often goes out with that man. Apart from the gym, they may feel bored and have a lot to say in private. When you are busy, you may secretly go somewhere for a date, and you don't even know how to make a room. You two have been together for a long time, and there are bound to be all kinds of shortcomings in front of her, and then she will think you are not good, and then a man will appear, even if that man cares about her a little (but as a boyfriend, you usually care about her enough, but she can't see it, which is called stingy), which makes her very excited.
And I lied to you at the beginning, indicating that her relationship with that man is in an ambiguous state. Why didn't she let you know? I'm afraid you'll be jealous and angry, which will cause them not to go to the gym together. They often go to the gym, and those in the gym will definitely think that the couple have been to the gym, which is quite suitable. At this time, your girlfriend will unconsciously regard him as a boyfriend, feel very proud and have a good impression on that man. That's how ambiguity comes about.
Why is that man so close to a girl? First, he is really free and willing to accompany your girlfriend to the gym instead of picking up girls to find a girlfriend. Second, he also has a girlfriend, who is really broad-minded, but if he has a girlfriend, can he have that much time?
So, tell her to stay away from him. You can go to the gym, but don't go with that man. Find a woman to be your friend in the gym and make an appointment to come to the gym together later. Why do you have to find a man? In a normal couple, if one of them is too close to the opposite sex, it is very reasonable for the other to make such a request.