Hi Chantal,

If he went on a date with another girl, that means it is not a monogamous relationship for him. Since he is open with you about it maybe you should ask yourself if you are in the same page with him. If you are monogamous to him and you expect the same from him you should talk about this with him and try to find a solution to avoid misunderstanding and your heart broken.
You can casually ask him if he is ok if you are the one who went out with another man. If he says he is ok with that, then it sounds like he is not making any serious commitment with you, at least you have an honest answer on how he perceive the relationship with you. If he says he does not want you to go out with another man then you can ask why he is being unfair by doing a thing to you that he wouldn’t want you to do to him.
Don’t compromise with something that hurts you. not worth it. Unless you can adjust with his lifestyle and still be happy.
And no, you are not over reacting, you just need to know how he feels about the relationship and decide whether you can live with it.