This thread is very interesting to me because my DH did exactly what you are asking the question about. He had a shiftbuddy/never a girlfriend maybe 19 years ago (we are early 40's). Me and DH have known each other since we were 12. We went to school together and got together late twenties. He had lived with 2 girls prior to me, but he had this one relationship, after school where he met her on and off for a period of 2 years. He treated her badly, it was on and off and he basically used her for when he felt like it. I know her brother but not really her (small town). He always talks about his exes respectfully and his regrets at being such a bollocks to her.
He got plastered drunk about 3 years ago (we had a couple of kids at that point) and I was pregnant with our third. He had gone out to meet a friend who I also knew from school. That friends girlfriend dropped him back and said they had done the dog on it drinkwise. He was wrecked, he said he was a bad person, didn't deserve to be a father, was crying; his parents came into it (not a great relationship) and I somehow managed to get him into bed). Next day about 5pm, he was showing me some message on his phone when one came in and I saw her name, talk about synchronicity). I asked why the hell is she texting you, read everything .... and he basically had texted her about being an arsehole and how sorry he was. She had texted back, DH we have gone through this before, i don't hold anything against you, why are you bringing it up again?
I lost the plot, I am his wife, why is he texting exes, I have not done the best by people/boyfriends before, I am not texting them, it looks like you want to hookup again/ you are making you're wife look like PRICK, WTF???/ why even bother, get over it/ not everyone is ever going to like you.
To this day it an argument I keep going back to. Do not do it. What the hell do you hope to gain? Or do you think that person was so dogedly in love with you, that all these years later they are still an option?