Two of the Gospels forbid divorce and remarriage. One contains the phrase 'except it be for fornication', but those who hold to the conservative view argue that it doesn't outright allow remarriage in the case of fornication. And none of these New Testament passages say a woman can divorce and remarry. The Matthew passage is about a man divorcing his wife, not the other way around. Roman Catholics go with the traditional view.
But there are some nuances. Marriages not entered into with the intention of marriage for life may not be considered accepted. Marriages between close relatives may be considered illegitimate. I'm not 100% sure on this, but historically, unconsummated marriages might not count.
Also, if a Roman Catholic marries a Protestant, if the Protestant is okay with children being raised Roman Catholic, a priest or bishop or whoever has the authority in their system to do so can sanctify it... or bless it... or whatever they call it, to recognize the marriage. But otherwise it is possible that such a marriage might be considered invalid.
There has been some 'corruption' where people get marriages annulled for various reasons. There have been cases historically where a royal will get a marriage to some reasonably distant marriage considered invalid and annulled. I read that a huge percentage of annulments are from people in the USA.
I remember back in the 1990's hearing someone talk about how one of his relatives was trying to get an annulment from a husband who was a drug addict from within the RCC. To me, this sounded like they might be trying to game the system. It was tough being married to this guy, so figure out a way to argue the case, but I just heard this second-hand and didn't know all the actual details.
If a marriage is between two Roman Catholics, generally the marriage is considered valid for life. If you divorce and remarry, you can be cut off from communion.
But I might say in some ways it is clearer and there may be less 'corruption' on this issue than with some Protestants. Some churches just accept any secular divorce whether it follows their own beliefs on divorce or not. At least they know what the rules are, and they don't accept a divorce on paper from the state if it doesn't conform with how they interpret the teaching of Christ on the issue. Not recognizing marriages to Protestants was a bit shocking to me when I read about that. That's a danger a Protestant marrying a Roman Catholic, thinking they believe in marriage for life, should be aware of.