Well, that is going to be a tough choice to make right there. Having to choose between someone you know you'd be happy with or someone new. What happened to end things between you and your ex? I think you should just follow whatever your heart says at that very moment...and try not to think too too much of the what if's just think about who you think you'd be happier with.

Good luck with everything!

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Never regret something from your past, everything happens for a reason.