Babe, it is not as rare to reminisce on old relationships. After all, they were part of your history.
This sort of nostalgia is common, and unless one never dated anybody else before marrying, at some point memories of old relationships will flashback when we hear a particular song, etc.
The thing is as long as you do not act upon this nostalgia by sharing memories with the guy, you're fine. So, like the others said... RUN, SHUT THIS DOOR, it is not worthy to jeopardize the stability of your marriage, or worse, break the trust between you and your DH for some idealized memory (most of the time we inflate how awesome the ex was...).
Most of all, rationalize and reflect... if that old bf of that great, he would be in your life now.
Focus on your new journey and on your great PRESENT life babeeeeeeee.
Height 5'5" -- HW 273/SW 269/CW159/1st Goal 169(Achieved!)/2nd Goal 150 (Normal BMI)
Starting BMI between 35 and 40ish? Join us on the Lightweights Board!