Without even reading...
Is this suspicious?
Yes
Is this abuse?
Yes
Is he cheating?
More than likely
AIBU not to give £5,000,000 for a wedding gift?
No
Would you see him again?
No
Is this a red flag?
No. It's probably a fucking parachute
Would you have paid this?
Unlikely
Are they / he / she being a CF?
I'd bank on it
Would this give you the ick?
I'm vomiting already
Any others?!