[Grandma to Clare:] "Goodness, Clare, why in the world would you want to marry such a person? Think of the children you would have! Popping into next week and back before breakfast." (1.7.6.)
From the traditional perspective of Clare's grandmother, Henry makes very bad husband material. Who, in her opinion, might make good husband material?
[Henry to Clare:] "You know that I love you. Will you marry me?" [Clare:] "Yes... Henry. […] But you know, really… I already have." (1.11.54)
Clare has known that she'd marry Henry since she was a little girl, so getting married to him isn't exactly a big deal. Plus, in Henry's future, he's already married to Clare. In this sense, they're already married somewhere in time.
[Richard DeTamble to Clare:] "Henry has chosen well […] He isn't calibrated to bring peace to anyone's life. In fact, he is in many ways the opposite of his mother. […] Tell me, Clare: why on earth would a lovely girl like you want to marry Henry?" (1.11.110.)
Henry's father thinks that his son's condition makes him very poor husband material. At the same time, he concedes that Clare is the right candidate for Henry because she loves him, which might help them overcome the obstacles in their marriage.
[Henry to Clare:] "Let's elope." [Clare:] "My parents would disown me." (1.12.11-13)
As much as Clare wants to be independent, she's still very much concerned about family tradition.
[Henry to Ben:] "So her parents have planned this huge wedding. […] I need to be there. I need to get through about eight hours of huge mind-boggling stress, without disappearing." (1.12.110.)
Henry fears that he won't be able to handle the pressures of the wedding because, to him, the whole thing is an ordeal. He only does it for Clare. How many couples consider their wedding an ordeal that only serves to please their families, you think?
[Clare:] In one part of this dream I was swimming in the ocean, I was a mermaid. [...] There was a boat on the surface of the ocean, […] and my mother was on it, all by herself. I swam up to her and she was surprised to see me there, she said, Why Clare, I thought you were getting married today, and I suddenly realized, the way you do in dreams, that I couldn't get married to Henry if I was a mermaid. (1.13.2)
Although their marriage is set by time, Clare still fears that obstacles will manage to prevent her from being with Henry. The water might represent the intangible nature of her relationship with Henry – she'll never be fully secure in his presence by her side.
[Janice to Clare:] "This isn't what your mom thinks we're doing." [Clare:] "Uh-uh. But it's my wedding. And my hair. And I give you a very large tip if you do it my way." (1.14.25-26)
The fact that Clare has to bribe Janice to do her hair according to her own wishes (on her own wedding day, no less!) suggests that her mother doesn't take kindly to someone disobeying her orders.
[Clare:] And so we are married… The apartment is a laboratory in which we conduct experiments, perform research on each other. We discover that Henry hates it when I absentmindedly clink my spoon against my teeth while reading the paper at breakfast. We agree that it is okay for me to listen to Joni Mitchell and it is okay for Henry to listen to The Shags as long as the other person isn't around. (2.1.1)
The closeness of the day-to-day experience of actually living together as a married couple makes Clare and Henry discover things they dislike about each other for the first time. But they try to accommodate each other's habits. So is marriage just a big compromise?
[Clare:] Our life together in this too-small apartment is punctuated by Henry's small absences. […] Sometimes it's frightening. […] Sometimes I wake up in the night and Henry is gone. […] When I was a child I looked forward to seeing Henry. Every visit was an event. Now every absence is a nonevent, a subtraction. […] Now I am afraid when he is gone. (2.1.6)
Being married to Henry and living with him has changed how Clare views his frequent travels. They have become an intrusion on their married life.
[Henry:] The hardest lesson is Clare's solitude. Sometimes I come home and Clare seems kind of irritated. (2.1.7)
Henry realizes that now that they live together, Clare sometimes feels like he's intruding on her space. She misses her alone time.