Would you - or could you - play nice with the ex?

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With the possibility of DH going into the military, this question popped into my head. His first and only GF before me was with him when he went into the service the first time. They had been broken up for about 2 years before I met him and he has not seen her in 7 years (we have been together 6). Every once in a blue moon she shoots him an email. If he was going I would be checking his email, he asked me if she happened to send an email, if I would bother replying. This is a girl who broke his heart, lied to him about multiple things and probably could have ruined his life if she so choose. So, as you can imagine, even if she is a saint now, I don't really care for her. Would I reply back to her, probably. Would I tell her where he is, maybe so. Heck, on a good day I would probably even give her his mailing address. I figure she only contacts him maybe once a year and he is married to me, has zero feeling left for her, so whats the harm? What would you do in that situation?