I Agree because what the guy needs in that situation is a lot of freedom whether it be to grieve for the lost love, to be alone, to go out with the guys, or to date other women--the point is, if you give him the freedom he needs, he will do what he needs to do, and if he does end up with the new woman, it will be because it's right, and there won't be any question.
I know because I've recently been in a similar situation, but in my case, the ex wanted to try again after we'd been dating for 3 mos. I had already told him to date whomever he wanted, but he was the one to request that we be sexually monogamous. When she came back, it broke my heart, but I only had to cry for a week before he'd figured out it wasn't going to work with her and was back to me.
He was honest and fair about the whole thing, which makes me think he's worth waitng for, but I'm still giving him lots of freedom right now. Bottom line is I'm happy with or without him, and comittment comes when the time is right.