Jesus quotes from the law in regards to how to divorce:
“If a man marries a woman who becomes displeasing to him because he finds something indecent about her, and he writes her a certificate of divorce, gives it to her and sends her from the house…” (Deuteronomy 24:1)
So Jesus quotes this scripture and then expands on this idea of divorce. He speaks of sexual immorality being the only thing that should be means for a divorce.
Jesus even goes so far to say that if a divorce occurs by any other means, the woman is then considered an adulterer, and any man who would marry the woman in the future would also be considered an adulterer.
The issue here, to me, is not necessarily the topic of divorce itself, but in how serious we should take the covenant we made before God when we get married. It should be taken seriously beforehand, and should be taken even more seriously after. A marriage is built on the promise before God that their relationship would continue to grow and be lead by God. Our marriages are important to God…make sure they are in a healthy place.
A Journey With Jesus 