Can a restaurant/bar refuse service to a customer when no disturbance has accrued?

A bar is a private establishment and the owner can choose who to serve and who not to serve as long as that decision is not made on the basis of race, color, gender, age, etc.

Yes, a bar or restaurant can refuse service if such refusal is not made on the basis of race, religion, age, or other protected class. In some locations, this includes sexual orientation. In this instance, it sounds l like the refusal to serve you was not based on any of these, but was based on the place not wanting to become the scene of any disturbance or bad vibes. The bar is siding with your ex-boyfriend and declaring the bar as his turf, and saying you are not welcome. Maybe he needs his space and wants to be able to socialize there with his friends. Obviously, the bar has a strong allegiance to him and not to you. They obviously feel like it would be best for all if you give him and his alliances some breathing space. And let's face it, if the place is packed with people who feel loyal to your ex-boyfriend, the situation is going to be awkward, at best. You feel insulted because you feel like you can handle yourself perfectly well, despite it being awkward. Well, guess what? Maybe your ex-boyfriend or his friends do not have so much self-control and things would get out of hand. The takeaway here is that when you date someone, if you allow yourself to become engulfed in their circle of friends, and their places, and their activities, you can be lost and bereft when the relationship ends. Try to date men who will also share your family and friends and activities and places. Let him invest in you, not just vice versa.