Hashirama calls him quote a gift from divine. Which wouldt happen if they were seeing one another as friends
Hashirama's brother and own father call him meeting with another boy as suspicious which adds extra proof to this assertion
Madara as he gets enveloped in kaguya's body. Thinks to himself where he went wrong.
Like these could very well be his last words and he's thinking about hashirama. If they were just friends then why would he think about hashirama here who would think about a friend like this as they are about to die??
What confirms this even more so would be madara says well guess that's okay, Implying he didt like it and was kinda shocked that he seen him as just that
It's also said that madara would allow nobody to touch him but hashirama and that he excites him
It's also said that madara waited years for hashirama which if they were just friends would not happen, The person would just move on from them normally
Hashirama also viscously protected madara even after he likely murdered all his siblings. So very clearly they are beyond just friends as he wouldt forgive him so easily elsewise
It's pretty much confirmed as madara was nervous about hashi seeing his junk
People still deny it, It's so obvious too