The second line of "The friendship between heroes and comrades is as deep as the sea"

Usually "love is as deep as the sea" corresponds to "favor is as heavy as a mountain". You can consider starting from this point in the second line. Note that this type of couplet must be combined with specific people, objects and events, and cannot be made out of jokes such as "father increases longevity" or "mother fills the whole family" just for the sake of neatness. So I'm not right about the specific second line, you should think about it yourself.