OMG, Serena and I know you both feel bad for him trying desperately to deal with his trust issues.
What is the status of DD and her BF? Are they still together? I know you mentioned her possibly leaving for the Military.
I would just "unplug" the phone and to HIM it will just ring and to you, you will hear nothing. I really do not how long you can do that, as I am sure you do not want the phone unplug 24/7. Wait until DAY TIME and if he continues to call, you need to tell him he needs to seriously "chill"!! And that he needs to stop calling you and that he and DD need to work this out alone in person.
Keep us posted.