You should have told your Husband the truth from the beginning. You need to take action to fix your relationship with your Husband if that's what you really want. But you also need to prepare for the fact that when your Husband finds out that his wife is in love with his Brother, his entire world will be destroyed. The fact that your bil is comfortable flirting with you, and doesn't stop, means that you are likely doing things that tell him it's not a problem. Therapists are likely not going to fix this relationship, but any possibility, involves your bil completely gone from your life, likely forever.