As a counsellor I have been contacted about family break ups and the heartache involved in one or other party having to give up the family pet. I notice that some solicitors are recommending a legal agreement in the event of a split so that both parties understand exactly what will happen. This is not something the Courts want to deal with and prefer it if couples seek mediation in the hope of not going to Court at all!
Ideally, couples will agree to share a pet. Many pets are sensitive to disagreements and life changes so their feelings should be taken into account. Pets are often devoted to the whole family and grieve noticably if circumstances change.