My boyfriend found an explicit text message from my ex-colleague

Even though I have explained that the whole thing was perfectly innocent, he is accusing me of undermining our relationship. How can I turn things around?Recently, I used my boyfriend’s spare phone while mine was broken. I downloaded all the essential apps, then thought I’d deleted them once I got my own phone back. But one evening, he received a message meant for me from an old work colleague. The content was sexual in nature and I ignored it. However, while absolutely nothing but a