There are three approaches in mood and med management in a relationship.
1. The healthy partner controls medication, reports symptoms to Dr.'s. The only times I've heard of this working in a healthy relationship is when the bipolar partner is temporarily too ill. Perhaps refusing medication or at risk of overdosing. In general, it is a bad situation. I've been in a relationship and have heard too many reports whenre this turned into physical violence.
2. The healthy partner sets boundaries and essentially gives the bipolar spouse "enough rope to hang himself." My relationship now is like this. It's my responsibility to take care of myself. If I am unwell, refusing treatment, etc., I know his patience is limited and he will end the relationship. This motivates me even more to stay as well as possible.
3. Some couples work it out as a team. This is completely unique to each couple. The healthy partner must take care to not enable unhealthy behavior patterns. My personal opinion is that the couple comes to an agreement, put in writing.
I am personally a fan of #2. It gives the healthy spouse an escape. I don't necessarily mean divorce or emotional separation. Especially when children are involved, it can be a tremendous relief for the bipolar spouse to live out of the family home, but visit and try to foster positive interaction.