These are two concepts don’t usually go together. Two people who love one another don’t necessarily need to have the same religious beliefs.
I’ve been relationships where she was (or still is) a die-hard Catholic or Protestant or non-religious at all (non-practicing Christian). Although at the time I wasn’t a practicing Catholic or Christian in general, there was usually some level of friction due to a religious (denominational) belief or another. The biggest question that’s come up has been what church (if any) to go to or what to do on Sunday morning.
These denominational differences also cause friction with the beliefs that a child would brought up with.
My first child has been raised Catholic, not as a simple social tag as I was raised, but as a deep spiritual belief. My two youngest boys (different relationship) are being raised without real (if any) religious beliefs. I’d try to teach them my beliefs or at least give them a broad background in theology and Christology.
The concept of sex and religion is a whole different mess all together. Depending on what a church (common spiritual beliefs of a social group who gather in a building in a given geographical area) teaches its congregation, sex can be good or evil to some degree within a specific group of norms (behaviors accepted and regulated by a social group). Within these social/religious/denominational differences a couple of different religious backgrounds may enjoy sex or not, experiment sexually (being kinky or simply naughty) or be subject to other limitations in their sexual behavior. From the animal point of view, one might consider cheating or simply do it to experience what his/her religious beliefs forces him/her to comply (sin).
For example, if you’re told that anal sex is the biggest taboo in your church, you might get curious and want to experience it at least once. If your partner doesn’t want to experience this behavior, you might consider doing so with someone else. Whether you do comply with your curiosity and urges outside your relationship, it’s a completely different issue all together (cheating, fornication, sin, etc).
Do I experiment? Of course I do. I don’t see any sexual behavior as a taboo.
Do I believe that sexual experimentation is a sin? I no longer know. I honestly don’t care.
Have I cheated? I had indeed.
Does it bother me that I had cheated? I no longer feel this way.
In general, I’m disconnected from these feelings. Nonetheless I want to be a good Christian.