What's my next course of action?
Ignore the situation. The guy barely remembers the name of all of our co workers. He'll forget eventually.
Buy a replacement umbrella, give it to him, blaming the replacement on how I had it next to another umbrella at the bar and picked up the wrong one (this exposes me lying to him last night)
Buy replacement umbrella and say that my boyfriend must have taken the wrong one to work one day and then left it there.
Buy replacement umbrella and leave it in his office one time when he's not there, never saying anything about it again.
Buy replacement umbrella and come clean.
Got a better idea?