Me and my boyfriend

Throughout our relationship people chatted a lot of shit to either of us about the other person making each other believe we’d cheated on each other and things like that when neither of us have ever done such a thing. We broke up because too many people were ruining things and for a month we didn’t talk however we got back together and was so good we were in such a good place until someone said as a joke I’d been talking to loads of boys when I wouldn’t ever do such a thing. How can I sort this situation out he thinks I’ve been talking to other boys and I don’t know how to prove to him it isn’t true x