When we read the marriage proposal and were asked to write about it I wrote, "She is too blind to see the ridiculousness of this proposal because she is using him just as much as he is using her. He uses her because she is the complete opposite of Rebecca and she uses him to live in Manderley and she realizes she may not find another husband. The narrator has seen the way he has acted and blown up before so she shouldn't be surprised if that were to keep happening. It's also unfair of him to propose to her because he is much older and has already been in love before and she won't be able to share the joy of experiencing first love when she's not someone elses." 

I just thought it was interesting that he would marry someone because she is the complete opposite of Rebecca and would be unable to love her. The fact that he can do that to someone just proves that he is not a good person and there will problems down the road.