What changed???? I guess both of them have different goals and plans and love faded away. Specially if the two are so goal oriented. But I guess they are not really so sure on what they entered into, the commitment is not that deep.
Well, there are a lot of reasons though, first is the financial reason. If money is lacking in a relationship the sweetness the love will be replaced with problems, shallow and immature thinking overflows and outdates their bond for each other.
It takes a lot of work really, one has to support the other specially if he or she is down.
Faith in God also is needed to make a long lasting relationship.

Thanks for the well wishes dear.

I feel bad for your friends though. They need to set aside their Ego's and let love prevail.