How would you deal with your spouse's change of heart on significant issues?
Sorry to learn of the predicament your friend is in Bella. It's great that she has an acquaintance like you to encourage her.
If I was in a similar situation with my spouse, I would try and negotiate a fair and equitable outcome with them. If they nonetheless wouldn't negotiate an acceptable compromise, or fulfil the original agreement, I would have to accept that outcome.
However, if the grief of not having my aspirations fulfilled was always near the surface, and unbearable, then I would consider separating from my spouse for a while for my own health reasons. That might seem extreme or manipulative to the other, but it might just cause them to stop and think about the impact their unfaithfulness to an agreement is having.
Unless there is an 'unacceptable' risk of spiritual, emotional, physical or financial distress associated with the outcome of an agreement, I personally feel it's pretty ordinary for anyone to opt out of a commitment they've made, particularly one of this kind.
In respect of changes in environment etc... a description of the wisdom of God comes to mind, which I hope to embrace and allow influence anything I do with any of my friendships/relationships. ie "...the wisdom from above is first pure, then peaceable, gentle, reasonable, full of mercy and good fruits, unwavering, without hypocrisy".
There is a dimension in marriage relationships which should always be considered when any decision is discussed and taken within it... ie, that the couple are no longer two, but one in flesh. Everything we do in our marriage relationship should be looked at through the filter: What impact will that have on my spouse and children, will it be beneficial to them, or will I be treating them unfairly, and therefore unlovingly.