Meaning: This means that your friendship is very strong and you believe it will last for a long time, maybe even forever.
Choice of Words: The word friendship means a close relationship between two or more people. Will is a modal verb that indicates that something is likely to happen. Never means not ever or at any time in the future. End means to come to an end or stop. When you put them together, "Our friendship will never end" means that your friendship will continue forever.
Our friendship is unbreakable.
Meaning: This means that you believe your friendship is very strong and will last no matter what challenges you face.
Choice of Words: The word unbreakable means something that cannot be broken or damaged. When you say "Our friendship is unbreakable," you mean that your friendship is so strong that nothing can destroy it.
Our friendship is eternal.
Meaning: This means that you believe your friendship will last for a very long time, maybe even forever.
Choice of Words: The word eternal means something that lasts forever or for a very long time. When you say "Our friendship is eternal," you mean that you believe your friendship will last forever.