Hi OP. Sorry you're having a shitty time. Things are actually worse when they are self inflicted (like hangovers) because you have a huge heap of guilt as well as having to deal with them.
For what it's worth, I was really drawn in by a lovely ex partners "I'm clean" lies! He was a long term friend and we went to college together. He was the only partner I didn't march to the clinic with me! But of course, sods law, he was the only one with a bloody sti!!
No intimacy in a relationship makes you feel crap and undervalued. Seeking it elsewhere, whilst morally wrong, is human. You made a mistake. It had consequences. Here you are.
You mentioned it may be from your husband, in which case I would wait for this guy's results. Make sure he's not faking them. Then, after treatment, I'm afraid it's time to tell your husband the truth.
If you are scared of his reaction, tell him somewhere public where you are out of earshot but he can not hurt you.
Lastly, I have also looked to suicide as a way out. I know you're feeling desperate and scared but you will be ok when you get to the other side of this.
The nights can be worse because you are tired and hormone levels are naturally higher. If you need them, call the Samaritans. They are amazing and will listen to you without judgement.
You're going to be ok.