A lengthy answer

First a summary of my church's position on divorce (this would be what I was taught as an Amercian Baptist and at Calvary Chapel). Marriage is sacred, and the only grounds for divorce is adultery. Divorced people are free to remarry. If the divorce was on the grounds of adultery, the aggrieved spouse is free immediately upon divorce. If they got divorced for other reasons, ideally the spouses should hold off on remarriage in the hopes of reconciliation. (But once one spouse remarries the other is free to do so). This is the most ideal of circumstances, they don't hold you to the reconciliation ideal once you're legally divorced... what is, is. (This would be for two Christian people).

So since that was a messy thing to write... if A&B aren't getting along that's not grounds for divorce. If A takes a mistress, then B has grounds for divorce (although the church will encourage forgiveness even so). Assuming A&B divorced because A was unfaithful, B is free to remarry. If they got divorced for "irreconcilable differences" neither are free to remarry. (With the obvious exception that starting a physical relationship with a third party would still qualify as adultery and would free the innocent spouse).

Paul's teachings are generally understood as an expansion on what Jesus said, not a contradiction. So - Jesus sets it down as "you can divorce for adultery" and Paul expands it to "but if you're both Christians obviously you're not in adultery so there's no reason to divorce, so don't".

For Christian/non-Christian marriages, officially they should never exist except that one spouse converted and the other didn't. As you know, we are specifically enjoined not to be unequally yoked with unbelievers. So... if A is married to B and B doesn't yet believe, A is to witness to B through good character (see 1Peter chp3). But if B doesn't want to be with A, B is to be allowed to depart. Reconciliation/remarriage is certainly desirable here - but if B is a non-Christian, the most likely thing is that B will immediately find a new relationship to enter into, which frees A to do likewise.

Young widows are told to remarry, older widows are told to stay single - at least as a recommendation. Mostly I think this applies to divorce as well... so if you are of childbearing age you're encouraged to get on with life, and if you're older, you're encouraged to throw that extra energy into the church. (This is because of the natural urges that women of childbearing age have, and in theory older women have the support of adult children, etc).

Okay so the metaphysical part... we are spoken of as *joined* to whomever we marry. Only... "marry" here is a euphemism for "having sexual relations with". Which makes sex a bonding, and is why adultery is grounds for divorce, whereas say non-support or abuse is only grounds for separation. 1 Corinthians 6:16 What? Know ye not that he who is joined to an harlot is one body? For two, saith he, shall be one flesh. So the act of sexual union creates another sort of union as well. (Which is why fornication is such a big deal, much bigger a deal than other sorts of sins of the flesh).

And yes, your friend sounds like a total cop-out to me. :p But maybe she just can't say, "Well I sinned in the past by getting that divorce, but I'm remarried now and am a faithful and true wife to the husband I have"? Starting that new relationship creates a new union, after all. And who among us is without sin?

So my own position... is pretty much the same as above, with a curiosity and respect to the mystical union involved in the creation of a sexual union. I know that being united horizontally is not the same as being married... but is that the case because those in this day who sleep together are refusing marriage or living a lie rather than because they don't have that union? There is a difference... but what makes it different?

Hm. Off topic that was.. For me, once you're married you should do everything you can to remain married. If you are able to forgive fornication (and if the fornicating spouse repents, which they might not!) then you should so that the original union can be remade. If not, then not. Being grumpy with your spouse isn't grounds for divorce - it is, however, good grounds to spend a lot more time in prayer and possibly in counselling.

And I'm being pestered by a seven year old who is delivering me imaginary pizzas... pepperoni and watermelon and sausage and cheese he says. So if this was unclear... pester me in turn. :)