Something or someone you couldn’t live without, because you’ve tried living without it.
This is obvious and cliche. But that would be my husband. He is wonderful and can always make me smile when I'm down. He and I have spent the first 2 (almost) years of our marriage differently than those outside the military. We've spent them completely dependent on one another without our families. Most newlyweds have their parents close by to go and talk to or to come over and help fix things, etc. We have been just us. We had our first Christmas 5000 miles away from our families.
As far as tried living without it, that would be deployment (and workups, and school) I've spent months without him and I can honestly say I much prefer him here.
It's like that movie The Wedding Date. I'd rather fight with him than make love with anyone else. :)