Răspuns:
Dear [Friend's name],
It is good to hear from you, and I am sorry about your difficult situation.
As much as I understand where Sara's feelings are coming from, it is your special day and you deserve to decide which people are going to be spending it with you. If you were to invite someone you don't like, and especially if the feeling is mutual, it might spoil everything and make your birthday an unpleasant memory. Nevertheless, Sara is your friend, and if Pete is important to her, perhaps you could make a compromise and meet her half-way. Who knows, maybe after the party you and Pete could get along better.
Whatever you decide, I hope you have a wonderful birthday and I wish you all the best.
Warm regards,
[Your name]
