If I've learned one thing about the Christian walk, it's that it is a daily activity rather than a one-and-done conversion. Every day I have to make the conscious decision to keep walking, growing, loving, etc. It's kayaking in a class 3 rapid; if you stop paddling, you will go backwards. There is no standing still when it comes to chasing after the heart of God. Yes, he is always pursuing, but we are also a very frivolous, forgetful people.
The point I am dancing around here is an issue I'm dealing with from people I'm close to.
Many Christian dating relationships focus on a very important aspect: purity. Christian couples will fight hard to have a Godly relationship with bible studies, prayer, accountability and restraint to keep kosher. Yes, purity is important... especially when God has brought you someone you want to respect, but also want to make open-mouthed kisses with. (Ha.) But what comes of it once the rings are on and the fight is over? You win! Go forth and multiply. But where is the motivation to pursue righteousness in light of the freedom you both now enjoy?
Lust is not the ultimate threat to Godly relationships.
Maybe more so in dating, but in marriage a new enemy rears its ugly head. This threat is much more delicate and crafty, and is a destroyer of worlds; selfishness and pride. They can creep in quietly and nestle in between the thrift-store furniture you've both recently purchased and there they grow and fester. Unless they are continuously being hunted and rooted out, they will grow and taint every bit of the old, new, borrowed, and blue. Like a mold. There may be symptoms that masquerade as unpleasant character flaws or personality quirks, but the putrescence below rages on. Don't be fooled, the struggles of selfishness in marriage are very much just as spiritual in nature as the lust you battled against in dating and should be approached the same way. Bible studies, prayer, accountability, and restraint. Both situations call for you to put the good of the other as top priority, and hope (but not expect) that the same grace will be granted you.
And above all, God heals all. No disease of the spirit can ever be conquered if God is not the center and the focus of both lives.
But what do I know? I've never been married. So maybe I'll stop talking now :)