wrong...?

Is it wrong to be friends with your ex...? It's been 3 1/2 years and he just contacted, I'm married now and very happy, but I've been feeling like my husband doesn't find me sexually attractive anymore. I've never cheated and I will never cheat because I love my husband, and all feelings towards this man are gone. And he says the same.... But it is wrong to be friends? He's in a happy relationship and so am I, and we were really good friends all those years ago... Honest opinions, I just don't know what to do....