Well, I finally got around to watching these last 2 episodes, and was certainly glad to not have them spoiled.
I was a little bored with Claire and the new beau, but their political differences became a sounding board for whether or not there was something deeper in terms of their personal world outlook, and value system. Whether they stay on course for a deeper relationship is up not to their political differences, but whether they truly understand one another, and accept their strengths and differences while also sharing common goals that include room for personal growth as time marches on.
Nate, as a flawed character, endured quite a journey these past 5 years. Coming out of his coma, he seized upon that old adage of "time is short" and dealt with as much of his personal happiness as possible after waking up. I think his talk with Brenda signified his growth to a level where he finally knew it was time to let go, and became open to the possibility of a new life of happiness with Maggie. Of course, this leaves a wake of family issues (Maya and the daughter Brenda is carrying) that Nate will never get a chance to deal with, but saying his peace, his intentions were known and as painful as his declaration was to Brenda, he knew letting go of his marriage was the right thing for both of them in the long run. For Nate, there was little value in staying married for the sake of the children if it meant dying a little more each and every day by staying married to someone who is diametrically opposed to him in spirit and world view.
Another hallmark of 6FU is how it portrays the value of marriage, and the impact it has on marriages that might have gone on too long (Ruth's marriage is the prime example, marrying young, but suffering quite a bit on personal growth for the sake of raising their 3 children with Nathaniel, and after she is widow, she spend a lot of time re-learning sides of herself that she left dormant for over 30 years during her marriage). And having Ruth and George rush into marriage, and showing us how marriage isn't something to be rushed into without truly finding a rock-solid bit of common ground and understanding, life in a marriage where there isn't enough revelation of oneself or the other person is a life that also brings on death a little sooner each and everyday the "relationship" continues to exist.
Rico and Vanessa finally come to terms with the hurt of infidelity, and the love that exists in spite of infidelity, but wanting that love while also wanting to protect oneself is not something that can co-exist in a committed long-term relationship without coming to terms with the feelings of infidelity and issues of emotional abandonment suffered by Vanessa.
3-4 years ago, Nate does the "right" thing in marrying Lisa, but in time the value of doing the "right" thing isn't enough to stoke the fires of a committed relationship, even during a year where Nate had no idea what happened to Lisa, but was able to put all those second-guesses away and move on. Having given up on his previous relationship with Brenda in order to marry Lisa, and then getting a second chance to re-connect with Brenda, even those initial smatterings of pure physical attraction and the yin-yang game of opposites attracting is put to the test, but in the end, that marriage had too many opposing views to endure, in spite of Brenda's pregnancy, and Nate was finally able to separate marriage from fatherhood, and made the best possible decision for his future family situation, even though Brenda's world was rocked, but I think deep down, she knows their marriage would not have endured in the long run given their divergent paths at this point in time, and because of their own personal baggage.
Interestingly enough, I think deep down, David and Keith do know what the other one is all about, and in spite of their differences, their relationship, even with all the bumps in the road, has endured quite a while, and I wouldn't foresee them not being able to overcome future obstacles in their relationship. The stress of being new parents is a good test for them as a couple, and I think they are in good position to resolve tough situations as their arise, even though it will highlight differences in their outlook, they know what is important (even in cases of infidelity, they've found ways to stay together for the right reason, and not split up for the reasons).
What any of these storylines is trying to say about committed relationship is up to the viewer, but as an examination of the cycle of life and death (with the funeral home business as a backdrop) of the relational aspect of each person who moves through life on this earth, this show has poses many situations, and allowing flawed people to make their decisions, impulsive or otherwise, and letting the viewers see the consequences of those decisions, and takes us on a similar journey of discovering yourself in various pieces from the multiple storylines that run through the television tapestry known as "Six Feet Under".