should i forgive and trust my husband again

He is having an online relationship with an ex girlfriend. They call each other on the phone, send each othere emails to his work and texts and even two of his fellow co workers were aware he was doing this but he didn't seem to care.I found the text messages which were smutty and he said he didn't know who it was and tried to cover it up (typical) but I found a later message and confrunted him and he said it was just stupid stuff but she says... I love you......
I have asked him to leave and go to counselling but he is taking his time and says its over and has removed his facebook page and says he is not talking to her anymore. How do i every trust him again?