should i tell my husband that... i once dated his brother?

From a man's perspective, I think you should inform your husband. Rather than letting your brother-in-law sharing it with your husband, I think it is better for you to let him know first. It may be earth-shaking for your husband, this took place before you met your husband, and I believe it will take some time for him to rationalize it. And to be sure: you really did not know that they were siblings, till your brother-in-law came back. So: attribute it to fate. Honestly, I hope this is a troll story. Otherwise I would advise you to seek professional's help... you shared you have an amazing husband, yet you hold thoughts/feelings to your brother-in-law; no right frame-of-mind would hold that "cute" thoughts or emotions when you have an amazing husband.

I would, rather than he were to find out himself in the future (it becomes you trying to hide something) whereas if you tell him now, it’s just gonna be a “idk he is your brother, I only knew it when he came back” thing. You can be like “OMG?!! He is your brother? Then go on and tell him your rs with his brother then assure him you have no more feelings for his brother.

I suggest should tell.. no secrets between a couple. if he finds out himself it's worse, he may think you have something to hide by not telling him

I would just be frank so he would also help me in awkward situations when meeting the brother. Rather tell early than later on

Nope. I won’t. And your bil probably thinks the same. And stop call him your ex, that mindset needs serious reboot.

u shld have told him at the start or even before the start of the relationship. n not wait 5 yrs later.

he'll find out eventually, secerets have a funny way of coming out. better it come from you.

I would be honest .. rather than he finding out and like you said, seed of doubt planted

I think you should tell him, rather than he find out one day.

it sounds like u hv nothing to hide :)