I can't go the theatre this weekend!

correction suggestion

I can't go to the theatre this weekend!

Dear David,

I hope you’re well. I’m writing to let you know that due to an unscheduled business trip, I won’t be able to go with you to the theatre this weekend. I’m truly sorry for telling you this at such a short notice and I hope you’ll accept my apologies.

The reason [why] that I can’t go to the theatre is that I’ve been asked to visit a client in Germany to help with a product launch, and I won’t be back until Monday. I wish I could have known about this trip earlier, but unfortunately my colleague (who is in charge of product launches in the central European countries) has been in a car accident, and therefore I have to take on his project commitments while he is in hospital.

What do you think about going to the cinema this week with Michael instead of with me? As you know he is a cinephile and I’m sure he’d be more than happy to join you. I thought I could offer my ticket to him and if you’d  you agree I could ask him to accompany you to the theatre. Once more, I’m sorry for not being able to go with you and I hope you’ll let me make it up to you by inviting you and Sara for dinner next Saturday after I come back from Germany.

Keep in touch
Adib

That was really good!

Tip: it looks like you need to revise the difference in meaning between "come" and "go". I am sure you know it already. It's all about two things: location and perspective.

Location

At the moment, you are not in the theatre. Let's say you are in your house. The theatre is in a place that is far from your current location. Therefore, due to your location, if you are still at home getting ready to leave, you would say you are about to go to the theatre. We say "go" because you are not there yet.

However, let's imagine I am in the theatre right now. I could phone you and say "please come to the theatre". That is because I am already there -- but you are not.

So, whether you say "come" or "go" depends on your current location.

Perspective

Whether you say "come" or "go" also depends on the perspective of the speaker.

The person giving the invitation says: "can you come with me?"

The person responding to the invitation says: "Yes, I can go with you" or "no, I'm sorry. I can't go with you."

So, your friend David would say: "Adib, I'm sorry to hear that you won't be able to come to the theatre with me."

You would say: "David, yes, I'm also sorry I won't be able to go to the theatre with you."

Hope this helps.