Sim Husband Gone, missing from game

@prismatikitty Did you exit the game without saving and then re-enter to see if he is still in the game (even if they have to re-do the ceremony)? If that does not work you could try going back to your next most recent save when he was in the game, and backward from there.

You can also check your in-game Library. There should be a copy of his household in your Library from when you created him. Unfortunately that version of him will be at the first created state, unless you saved a later version of him to the Library. Please also keep in mind that any household saved to the Library only preserves the relationships with any other Sims saved with them to the library in the same household. (So... if you place a Sim from your library they will enter the game only with those relationships, skills, etc., intact.)

Once you find him...

• Confirm in Manage Households that he is in your 'Favorite' households (if not click the heart on his household to move him to favorite households). This should protect him from culling. 
• You could then merge him into her household in Manage Households. This should make it easy for them to build their relationship.  (Once he's merged into her household they should automatically be at 50% friendship.)
• Make sure her doors are unlocked to all household members, not just her.
• Once they get married you shouldn't need to worry about merging households or anything, in case something is acting up for them in this aspect, since they already live together.

If the process is still acting up you may want to check your Mods/CC if you have any. I can provide directions if you need them.

You could also try a game repair, if you like, if this or any other aspects of the game seem to be acting up. Most of the time it's a hail Mary pass, but it can't hurt, and sometimes it helps, depending on the cause: