Hearing Oscar's invitation to get married made the fog in Lisa's head just disappear. Her mind immediately returned when the two of them were married. There are no flowers, rings, chocolates, or romantic proposals as couples usually do.
Their previous marriage looked like a fake marriage.
There is only a marriage certificate that can be used as evidence that they are husband and wife. Apart from that, nothing else can prove their relationship at that time.
Now Oscar did the same thing and asked her to marry him as if getting married was an easy thing and no need to think about it any further. Lisa actually wanted to marry that man, but she didn't want what happened a few years ago to happen again.
It's not that she didn't love the man or refused to marry Oscar again, it's just…she's still not ready.