I think its important to tell your husband whats happened. I know sometimes people have affairs and don't tell them...but I don't think its fair to deceive the other person in that way - they should be able to make the decision as to whether they want to be with you + work through it, or leave.
I know therapy/counselling is expensive, but a lot of places are offering discounts at the moment for NHS workers. Check out MYNDUP - I believe they have volunteers who are offering free sessions for NHS staff. I'm not sure how many sessions that would entail, but its a start and hopefully it'll work for you.
I would say just work on dealing with one thing at a time. Maybe end the affairs first, then speak to your husband about whats happened, and then check in with a counsellor/therapist and either work through the affairs first, or the COVID-related stress.