Well, sometimes "fake it till you make it" works, so definitely try it!
But in an ideal universe you'd tackle this anxiety itself because it can be a monster and could grow and attack other things (like, one day, your kids going out somewhere - trust me, they won't appreciate it).
FWIW I agree with posters who say it's polite to tell your partner your plans, and basic decency in a partnership to stick to them, especially when there are pregnancies and tiny children involved.
But I don't think it's about being a "cool wife" as such when things go wrong. They way you say "whether he's coming home", that's your anxiety and paranoia talking, and it's lying to you by saying he might not. He's always come home so far, all his stuff is there, you're there, you have a family together, what are the real chances of him not doing so?
God, I know this is easier said than done - I once had a full-on panic attack because DH went for a walk, had his phone on silent, and I was convinced he'd been killed in an accident or something.
I had to work at "letting" him go out (because it is a control issue) without knowing when he would be back, and without a phone, and honestly it was hard and sometimes still is - but it's gotten easier. And when I've been cross, it's genuinely been at myself not him. He's not doing anything wrong by having a life. But anxiety is a horrible liar and the more you give in and placate it, the worse it gets.
(Also, enjoy the Ben and Jerry's, they stopped selling it near us, outrageous!! )