Sorry to hear that, Lexy. I've lost keys twice while diving.
The first time was in Lover's Cove and the key belonged to my girlfriend's company truck! The next day I went back to dive for it and discovered someone had found it and placed it on the railing there. Lucky me.
The second time I was diving fairly shallow (20-30 ft) in Descanso Bay (where the Valiant rests). I lost my own company car key (had stupidly left it in my bathing suit and wasn't wearing a wetsuit). When I realized it was gone, I remembered feeling something lightly hit my thigh as I dove down on a kelp "plant." I went back the next day to look around but couldn't see the key anywhere I had been. I went back to that kelp "plant" and was looking around on the bottom when I turned me head sideways. In my line-of-sight were the keys, nicely tucked under a small rock outcrop out of sight unless you looked sideways!
I no longer have a vehicle here and now keep my house key in my bathing suit pocket UNDER a wetsuit... and a spare at home in case.
Good luck getting yours back, Lexy.