I don't think it would be a good idea to tell my husband that my ex gave me an expensive jacket as a gift.
Your probably right, but why do you want to keep it a secret?
It was a surprise gift and I don't want my husband to know.
It'd be hurtful to your husband if he got to know that you were still in touch your ex and received a gift. On top of that you want to keep it a secret which will harm your marriage so you better be honest about it with him.
OK I'll tell my husband, you're right.
It's smarter to tell your husband about the gift from your ex, especially since you did nothing wrong and your just trying to be transparent.  Your husband should respect you more for telling him as opposed to keeping it a secret.