Let him know that you understand if there are reasons you cannot attend the wedding, but also share your emotions and how much it means to you to be a part of his special day.
Respect their decision: If there are valid reasons for not being invited to the wedding, try to understand and respect their decision. There could be various factors influencing the guest list, and it might not be a reflection of your friendship.
Offer support: Let your friend know that you'll be there for him regardless of whether you can attend the wedding or not. Offer your support and help during the wedding planning process or even afterwards, during their married life.
Plan a separate celebration: If you are close to the groom and would like to celebrate together, you can plan a separate get-together or party to celebrate their marriage. This can be a great way to show your friendship and celebrate the occasion even if you couldn't attend the wedding.
Stay positive and understanding: Avoid letting any negative feelings or resentment affect your friendship. Remember that weddings can be complex events with various constraints, and your friend's decision may not be personal.
Focus on the bigger picture: Weddings are one-day events, and the true essence of your friendship lies beyond this occasion. Cherish the memories you've created together and look forward to making more in the future.
Remember, every situation is unique, so adjust your approach based on your friend's response and the nature of your relationship. Being understanding and supportive will go a long way in maintaining a healthy friendship.