This is really too much. I totally understand you having doubts about the safety of this arrangement. Me, personally - if I were you, I would not be afraid of his love or any jealousy, but mostly of the STDs and your husband’s responsibility. But it is possible to regain trust. I did the same thing, I was manic and had unprotected sex while being drunk. I didn’t catch any STD, but afterwards I SWORE to myself that it will not EVER happen again. My boyfriend doesn’t know. I am aware of the fact that it is unfair but I was too ashamed to confess. And the whole experience was too traumatizing for me. So I just closed this door in my head.
On the other hand - my boyfriend was insensitive with me and my jealousy at the beginning of our relationship long time ago. He basically introduced his other relations into our relationships and subconsciously provoked me with sharing everything. I felt insecure and heartbroken. Everything changed when he started to treat our relationship seriously and love came in, he is a different person now, but those fears still haunt me sometimes.
But anyway - we talk a lot, share doubts, give each other time. It helps.
I am not sure whether your husband can get some responsibility after such experience. The problem is the STD. I am sure that he regrets, but I don’t know if he is a person to be trusted again. You probably know this better than us here. Give yoursef time, think it through, let yourself be really mad. But don’t open the relationship until you feel safe and you are both healthy.
I hope you haven’t catch anything. Best wishes.