How can I expain that it wasn't me sending the texts?

My friend took my phone and sent the message, "I love you" to a few people on my contacts. One girl replied (who I really like), and he started saying stuff and being weird. But, he went too far and she asked him to delete her number from my phone. Even though he admitted to not being me, she didn't care.

So now I don't know what I'm supposed to do. I got my phone back, but she won't answer me.

Honestly, you need to talk to her in person and tell her that. If she doesn't believe you then she's not worth it.