Yes, it is generally considered rude to attend someone's wedding if you were not invited. Wedding invitations are carefully planned by the couple, taking into account factors such as the venue capacity, budget, and their desire for an intimate or specific guest list. If you were not included on the invitation list, it's important to respect their wishes and not attend the wedding.
Crashing a wedding (showing up uninvited) can put the couple and their families in an awkward position and may cause discomfort or inconvenience during their special day. Additionally, it can be seen as disrespectful and may strain your relationship with the couple.
If you were not invited to a wedding but your significant other was, it's best to discuss the situation with your partner and understand their perspective. They might be able to explain the reasons behind the decision or offer insights into the couple's preferences. Ultimately, it's essential to respect the couple's wishes and celebrate their union in a way that is appropriate and respectful of their plans. If you feel a strong desire to be part of the celebration, consider reaching out to the couple directly to express your well-wishes and celebrate with them separately at a later time.