Given that the majority culture is Christian, many of us never thought of actively taking up some other religion, even when we were thoroughly burned out on the churches we were raised in, disillusioned with their policies and practices, and finding ourselves strongly disagreeing with their philosophy, simply because we had not seen any other attractive options. So that portion of the population which is nominally Christian, who respond that way out of habit but are not actually committed to it, is quite substantial. When I talk to other Wiccans, I find that most of us came from that portion of the population. Only a tiny minority says that their parents were very open-minded about religion and let them try out various churches and spiritual practices without pressuring them. And only now are we beginning to see a younger generation who have grown up with Pagan parents and have been exposed to sabbat circles and gatherings their entire lives.
I have also known several couples who took up the practice together, and those who have children include their children in their circles and teach them our ways. In all of these cases, the couples are still together, although I am well aware that Wiccan and Pagan couples also get divorced. I can only go by my own observation, but when I call to mind the couples that practice together, I see lots of the same couples together year after year at gatherings and events, with relatively few who have separated or divorced. Most of the Wiccans I know who have divorced or separated are those where one was Wiccan and the other was Christian. Of course, since we have no reliable statistics on Wiccans and Pagans, we really have no statistical facts about how our marriage and divorce rates match up to the population in general.
Couples who share rituals and activities together have a number of opportunities to bond and build stronger relationships. Think about the joy, heightened awareness, and deep resonance we find in doing rituals together, from sabbats to full moons to initiations, handfastings, or other rites of passage. How would it feel to come home from one of these events, feeling wonderful and profoundly moved, and share a bed with a partner who couldn't care less about it?
Practices unique to Pagans, such as sex magic, can help form closer bonds between a couple. Wicca and many other Pagan religions have a culture that embraces a more liberated attitude toward concepts from birth control to handfastings for gays and lesbians to polyamory. That stands in strong contrast to the Christian religions that are officially against birth control, gay marriage, women clergy, and advocate the teaching of abstinence-only sex education.
There are also many other Wiccan ways that can be practiced together. You could study tarot, astrology, or healing together. Tend the herb garden together, drum and sing together. You might spend evenings making magical things together, crafting your own incenses, oils, soaps, candles, teas, and other things. You've got rituals to do together. Life is very full when you have such an array of common interests and activities.
At the root of this question is the fact that there really are differences in what religious beliefs we choose to embrace. If the Christian spouse is a "Christmas and Easter" sort of Christian who regards a partner's interest in Wicca as a sort of a hobby on a par with belonging to a book club or tennis league, or simply regarding it as the "girls night out" or "boys night out," then there will probably be no serious disagreements over the issue of religion. However, if each party really has a strong belief in his or her religion, then there are bound to be irreconcilable differences.
Consider that in order to be a Christian, you have to accept Christ as your savior, but Wiccans don't believe in saviors. Christians believe that we need to be saved because we are born sinners, but Wiccans don't believe in sin. Christians believe that immediately after death, we are judged and sent to heaven or hell, whereas Wiccans believe in reincarnation. Christians believe that if they do good things, it is because they are being influenced by God, and if they do bad things, they are being influenced by Satan. Wiccans believe that they are always responsible for their own actions. The Christian who insists on referring to God strictly as a male entity will no doubt get arguments from the spouse who worships a Goddess as well as a God. The Christian who chooses to tithe 10 percent of the family income to their church will not find agreement from the Wiccan spouse who is used to only paying a modest fee for classes or coven dues. Strong beliefs in these philosophical differences will result in disagreements between partners.
We Wiccans share a desire for loving personal partnerships the same as most other people. You might consider that this is one of the tests the God and Goddess place in our path to see just how dedicated we really are. Some seekers revert to being solitaries and others may even see if other religions or spiritual paths offer greener pastures for finding a partner. Others of us find our partners because we stick with our chosen path and eventually find a suitable mate through dedication and confidence that the God and Goddess will take care of us, even though in some cases, partnerships form rapidly, and in other cases, the right partner takes a long time to manifest, even if we have done a magical ritual for this purpose.