I'm trying to marry every bachelor and bachelorette, so I want to give bouquets to the next person I'm going to marry after I divorce the current spouse.
I just want to know if the spouse will know about it and get jealous or smth
You can do that, your spouse may comment on it or become jealous (which is their prerogative, because you are effectively being unfaithful), but otherwise nothing will happen. It's best to do it on a high-luck day, then there's a good chance that not even your spouse will comment.
But you shouldn't set the moral bar too high in this game. Actually, the bouquet should be rejected if you are already married, but it isn't; on the contrary. However, the special 10-heart event with all the boys or girls is only triggered if you are not yet married.