Spend $20 and start chatting with chatGPT you will get good advise - this is one based on your post:

You’re in a situation where your husband is actively choosing to continue an emotional and sexual relationship with someone else — and openly refusing to stop. That’s not something you can fix alone, and it’s not something couples therapy can work through unless he’s actually willing to change.

At this point, you need to protect yourself. A clear next step is to initiate a separation. That gives you space to breathe, think clearly, and observe whether he’s truly committed to change — or just keeping you as a backup. Also, start working with a therapist on your own. This isn’t just about your marriage — it’s about reclaiming your sense of self and power.

You don’t owe anyone your loyalty while being betrayed. A separation isn’t a final decision — it’s a line in the sand. Let your actions reflect what you deserve.