What should I do?

The biggest danger and mistake is that you are keeping this a secret from your husband.

It's time you tell your husband. He will somehow get knowledge of this, so best you tell him yourself.

If this man is just a friend than you wouldn't be keeping it a secret from your husband.

So, do you still love your ex? Is he more than a friend and you're just fooling yourself into thinking that he's not? That's what it sounds like to me.

Either tell your husband that you're friends with your ex, or tell your ex that you can't be friends with him because you're married and you're lying to your husband.

I agree with Altenweg, are you sure that there is not more going here than just friendship? It's not your frienship that is so wrong but the fact that you are keeping it a secret from your husband is. As hard as it may be to tell him now, how do you think he is going to take it whe he eventually finds out all by himself?

You saved me a lot of typing. I agree 100%!