Darling, I am glad to see you are handling this so well. You are strong. Dont ever stop believeing it.
I would not warn him about his new simcard. I would have it ready for him, and just pop it in his phone and say "there you go, new sim, new number, new life". You dont want him to prepare by writing her number down on a piece of paper prior to ceremoniously handing over his old sim.
Could you withdraw his "mobile phone privilege" for a while?
Please dont call the OW again. She seems like an airhead, not worth your time. But at least, now you KNOW she is an airhead, and nothing like you at all.
This is probably going to sound utterly studpid, but looking back, he has relied so much on you, your strength, your way of handling things, being away from you must really have thrown him. Would you ever consider moving into quarters with him, or near his next posting so he can come home rather than staying in the mess.
I have a friend (yes another one of those) who used to go and stay in some mess somewhere, due to her line of work. She wasnt exactly army, but worked closely with them on projects, and she had the attitude "No need to plan going home, there will always be a bed for me with some bloke at the mess." I am very non-judgemental.
Diorrific, I didnt really use to be a spangled evening, it is code.