When is a relationship or marriage over ?
It's a tough question to answer and there are probably many good answers.
It's over when it no longer serves you.
When do you re-pot a plant ?
When it's outgrown the pot.
Aside from being united in marriage, you are also an individual with your own needs and must remain true to yourself, otherwise you can whither and die and worst scenario bring your partner down with you.
As in gardening, so in repationships; weeding and repotting and pruning are necessary, indeed, essential for healthy growth