Boyfriends friend told him that I text him, now it's over?😢

My boyfriends friend told him I text him which I haven't, and automatically my bf believes him and has said it's over😢 he said that when he goes back he wants proof and his friend said 'uh yeah I declined it anyway'. Which should have proved to my bf that he was lying because when u decline a message on instagram it deletes! he knew he didn't really have proof of me texting him 😢 he's just gone back to his friend to get 'proof' and I don't know if he's going to come back😢 how can I make him believe me I haven't done anything wrong 😢💔 we have been so good lately and have a 5 month old baby together and he's going to finish with me over a petty little lie? 😔