sharksscareme this is really sad for you and must be very hard to cope with.
I don't know for sure what I would do but I would find it very hard to trust him again.
I don't know what the nature of the work experience is but whatever it is this is totally inappaoprite.
It's not your fault and I hope you will find somene to talk to in a real life, a counsellor maybe, who can help you work through your feelings.
I am sorry for the girl, she is very young and your dh should not have engaged in this type of texting etc.
OP please look after yourself.
I am not sure how old you are, but you were talking about kids later in life. I had my dd at 39 and adopted at 45.
Thinking of you, this sounds very, very hard. 
Mrsrochesterscat
I am so sorry to hear about your daughter. 