Married to a Bipolar person, What should I do?

My wife and I have been married 6 years. we have a 4 year old child together. We have split up once before in the past for 3 months and now she says she is leaving again. Everything seem to be fine ,she is doing good on her job.we have been getting along well. So I thought. She goes thru mood swings One day she loves me the next she wants to run away. I Love her, but when she gets in one of these modes there is no talking to her. she's right and thats it. I know she will want to come back eventually, but how much heartache can I take . I feel if we did get back together its only a matter of time before she wants to run away again. and its really starting to effect me. I really care about her , but i'm at my wits end and its becoming too much for me to take. I need some sound advice on this. what should I do?