Is it ok for my boyfriend to take other girls out to dinner and drinks?

My boyfriend is in his late 30's. I am in my mid 20's. When we met, he was always with women. He has a lot of female friends (most of whom are beautiful women who are also in their mid to late 20's) that he would invite out to dinner and drinks (he always pays). Every night he was with different women. At times, he would be the only man at a table of 10 women. After we started dating, he never again mentioned spending time with these women. While I didn't think he stopped seeing them altogether, I figured that he was no longer taking them out to dinner on a nightly basis (I work nights). Recently, a staff member at a restaurant that he and I frequent pulled me aside and told me that they felt I should know that he has been bringing other women in almost every night. They said it seems platonic but that his behavior was questionable enough to raise a concern in their mind. Am I wrong for letting this bother me? Should he have let me know that this was going on? I have never been formally introduced to any of these women. Perhaps if I knew them and was invited to these "outings" I would be less suspicious of his intentions.