Yoongi is always busy with his work, he needs to relieve his stress, he sleeps with literally everyone but Jimin, his own husband, he doesn't need to keep this as a secret to Jimin, he won't realize it anyway. On the other hand, Jimin is always bubbly, at least that's what he looks like to his friends, he knows that Yoongi is being unfaithful, but he pretends to be dense, not wanting to ruin their (not so) 'happily' marriage life.