Look at you, you're a hard-working, responsible guy. You take your vitamins (two different kinds!), you floss, and you jog even though it makes you feel like your knees are going to fall off. Why then would you go and do something as unhealthy as hooking up with your ex? Seems kinda counterintuitive, doesn't it? 

A smart, well-adjusted dude wouldn't invite drama into this life and willingly disrupt his mental serenity. Sex with an attractive woman is wonderful, but this one happens to come with as many strings as there are strands of hair attached to her head. Despite your best intentions, getting naked together will trudge up all of those memories—the ugly ones, the beautiful ones, and the really ugly ones. Give your ex a hug, wish her well, and be on your way, because in the end, that's the best decision you can make for your mental health.