Bfs cousin

So me and my bf broke up and his cousin slid into my dms, I told me bf when it happened and he said Idc do what u want move on, so I replied! When I mean the convos me and this cousin was dry not even Vaseline could fix it 3 day replies and we was talking about nothing but uni and gym. Me and my bf got back together then it got brought up a few weeks later. Now he’s ended things with me because his cousin made false accusations and I don’t know what to do I just want my bf back ! I understand why he’s pissed off but it’s also his fault and his cousins fault also !