If it's no inconvenience to you then do it. You need to start thinking of her as a coparent, not your W. The long and short of it is that you are upset because she's going with OM. If she was going to visit a sick friend or family member I'm sure you wouldn't care, right? You need to get yourself to a point where there is no difference to you. You shouldn't care whether she's going to see a sick friend or going to jump naked out of a plane. All you should care about is your schedule and whether you can accommodate her request or not. If you can't then fine, tell her that. But don't refuse just because you don't like what she's doing with her time, that's not your business anymore. I'm not saying you need to approve of what she's doing, I'm just saying you have got to quit letting it affect you so deeply. Make everything about YOU and your D. Leave your W alone to make or break her own life.
Great advice.
Everybody hurts. It's part of life. Don't miss the good stuff.