Italian jasmine shrub starting to struggle

Hello!

I've an Italian jasmine shrub that has been here for a lot longer than I have lived here. I'd guess at least 12 years. Over time, I suspect the conditions have grown less favourable to it as it's been set in to more and more shade from neighbouring trees. That said, it's always looked great till this year. Large amounts of dieback, next to no flowers and looking really thin. I obviously can't move it, and there is not a lot I can do about the neighbours trees, and in fairness, they do keep them under control.

I'm on sandy soil, but the soil is not too dry where the shrub is at that end of the garden. Any ideas anyone? Got a few photos of they help.

Thanks in advance!