Veneers have shifted, will a retainer help? (Photos)

I’ve had a nightmare with veneers. I had some done last year that kept falling off, etc. I managed to get some £ back & earlier this year I went to a reputable cosmetic dentist. I was never given a retainer for my top teeth, only the bottom. I have now realised that my two front veneers have moved apart slightly. The dentist has told me they will make a retainer that will make my veneers tighter, will this really work? I’ve provided a before and after pic. I loved them before :(