Is it wrong to have a (relationship) back-up plan?

So, the saying "A bird in the hand beats two in the bush" is right along the lines of "Better the devil you know than the devil you don't" - basically meaning stick with what you've got, who knows what's out there. But what if it's not that black and white? Take a look at today's cases.

Case 1) Holly has been married for six years to Daniel. They dated for two years before that. Her relationship has been... rocky. Holly believes that she is a good person and her husband is a good person. But together they are a powderkeg of drama, escalating fights, declining cocoa stirring, piss-poor communication. Over a year ago, she separated from her husband. During the separation, she met Lawrence. It was light a whole new world for her. No drama, all light and laughter, bubbly cocoa. And then Daniel came back with promises and pleas. She felt she owed it to him to give it another chance. She sorta broke it off with Lawrence asking for time and distance while she sees what's up with Daniel. 

Case 2) Ken is dating a lovely girl named Kim. He's in love with Kim but she's not ready to commit. He's proposed twice but Kim says she needs "just a little more time" before she takes the next step. Ken has a good friend named Leena. Lately, there's been a vibe between them. Neither of them have acted on it though they've acknowledged that the vibe is there.

So... what to do?

Personally, I don't like confusion. I need clarity and consistency in my relationships. That whole "torn between two lovers" vibe has never been for me. Then again, I'm very much a "dance with the one who brung ya" kinda girl. 

What do you think, BougieLand? Should Holly ride it out with Daniel? Should Ken give Kim all the time and space in the world to figure out whatever she's figuring? What would you do in these situations? Do tell...