Dear Sam,
I am so incredibly sorry to let you down, but I am afraid I will not be able to join you at the theatre this coming Friday night as we had planned.
I feel terrible about this, especially since you went to the trouble of booking the tickets weeks ago. Unfortunately, an urgent work deadline has just been dropped on my desk, and my manager has insisted that I stay late all week to finalise a project report. It is completely unexpected, and I am genuinely disappointed that I have to miss the show.
Regarding the extra ticket, please do not worry about losing money on it. Since it is such a popular performance, I am sure you could easily sell it to another friend or perhaps post it on our local social media group; there is always someone looking for a last-minute seat. If you cannot find anyone, please let me know, and I will happily reimburse you for the cost of my ticket immediately.
I hope you still manage to enjoy the performance despite the change of plans. Let’s catch up properly once this busy period passes.
Best wishes,
Alex