He was is a call spread... and got assigned in his short leg. So he is not covered.... he lost 63 cents... will only make that back when the stock drops, since he's short delta's now... short 100 (by being assigned in his call) and long 90ish...
I refer to the put, since you have to look at put call parity. During dividends, if you hold an ITM call... if you exercise, you get the dividend but give up the remaining time premium... which is the same time premium as in the put (P/C-parity). So in reverse, if you don't exercise... you lose the dividend but gain the remaining time premium.
In OP's case. Dividend was 73 cent. The 77,50 put is currently about 10 cents, which is the remaining time premium... so he's lost 63 cent due to him not exercising.
It's the way it works... I can explain further if you like.. but now I'm going home for dinner.
Hmmn that's an interesting thought. I never looked at the put-call parity that way in terms of time premium. I always thought time premium can change depending on how much delta and vega changes via how much the underlying moves before expiration.
Have a good dinner!