Anyone who is mad that you missed their wedding to pursue a potentially life changing career opportunity is someone whose wedding you'd want to miss anyhow.
There's nothing inherently selfish in pursuing goals, even in the case when it means that you have to sacrifice some previously planned activities that are meaningful to you. The virtue of sacrificing your own interests for the sake of relatively meaningless social engagements is non-existent. I would argue the virtue exists much more in sacrificing for the pursuit of that which is meaningful to you. A well-written and sincere card can allay any negativity between you and your friend.