I agree with what is being said - this is an issue between you and your husband, as the "other woman" in a relationship, i would not, for one moment back off because his wife contacted me - whether she was nice about it or nasty.
If a married man approaches a woman on whatever level - but certainly more than a friendship one if he wants to be in her warm bed - he is not as happy at home as you think and perhaps you need to look at your "lovey" relationship in the light of the possible evidence that you have unearthed.................believe me happy men dont stray AT ALL.
So, if he is unhappy enough within your marriage to look elsewhere, then get over it being HIS issue...............because its not, its BOTH of you..........so you need some honesty with yourself and with him about what is wrong because until you do you wont know how serious this issue really is................. look at your own dynamics
Good luck