Who is the one here breaking up the marriage ?
In your example, it is the JW mate who is initiating the divorce. But only in the example that you have given. I would not be generalizing that it is always the JW who initiates the divorce.
Isn`t it in the majority of cases the JW who ends the marriage ? because of religious differences ?
Can't say conclusively unless we have studies that establish this; which we don't have. We can say only from the experiences that we have personally seen. But the cases may wary and there may be many other underlying problems in the marriage other than religious differences.
I have personally seen many couples who have kept their marriage intact even though one of them have left JW's. There are many on this board too.
Is it even a scriptural reason for divorce differences of a religion.?
No
The Jehovah`s Witnesses blame the one who rejects the WT beliefs as the one who has split up the marriage
I would say that whenever any marriage breaks for whatever reason, both the parties blame each other.
Do Jehovah`s Witnesses break up marriages or do those non believing spouses break up marriages of Jehovah`s Witnesses.?
Each marriage is unique and hence this differs case to case. It is next to impossible to generalize because in a broken marriage, both will blame each other for their troubles.