Here's what I took from it, and I think its definitely open to interpretation. And bear with me, since I am still turning this movie over in my head.
I think the overall theme, is that communication is what unites people/beings together.
From there, it goes into how we as humans perceive time vs. how they the aliens do. The aliens have a higher level of consciousness, which allow then to know that time is not linear. It exists all at once, hence all the circle symmetry. There's no beginning, no middle or end. It all just equally exists as once. Now this is a wild concept to digest since its so far removed from our own experience, but wildly fascinating in my opinion.
Current evidence shows that time is indeed relative, so to go one step further to suggest its non-linear as well is interesting postulation, and one that future evidence will enlighten us further on whether its a possibility or not. But back to the film.
The aliens are able to perceive their high level consciousness through their language, so the more she learns and understands their language, the more she is able to perceive time as they do. First in her dreams and then right out in the open during the day. Its like a blind person being able to start to see for the first time. Visual stimuli was there all along, but they just weren't able to perceive it. So to her, the future was there all along, but she now is able to perceive it for the first time.
They do marry and he asks "do you want to make a baby". The reason why he gets pissed is that she already knew the baby would get sick and die but let him knock her up anyway and never told him beforehand, or included him in this decision. When she does eventually tell him, he feels betrayed and I would to. So through that betrayal, he loses his love for her and leaves, unable to watch his daughter die. He distances himself so it doesn't hurt as much, but it would have never hurt at all if he would have just been included in the decision from the beginning.
I think if she would have been up front with him, he would has seen how much it meant for her to experience her child's life and probably would have gone through with it, but they would have done it together as a unit. Not how she did it, betraying him and all.
I don't think it happens again and again. I think that its happening right now and those moments last in eternity, but I don't even really know for sure.