Ready to lock it down

Okay so I'm in an open relationship between 2 guys one that I used to date and the other whom I just started seeing. I like both of them and at times I catch myself being with just one of them but then it's like the next day I just want to be with the other one. I want to be with just one because my emotions can't handle the situation but they're both really nice guys and I care about them both I don't know what to do. How do I know which one to chose?