People Cheat in good marriages. Cheating is about the cheater - it’s a choice that someone makes. I think you are still in the fog.
All marriages have ups and downs - bereavements, illness, stress - but cheating is a choice. You break your vows through choice. You choose to give up your honesty and integrity for cheap thrills and ego kibbles. I can’t imagine any bloke is worth that tbh.
However you say ‘it would kill your husband’. I am guessing you mean he would be devastated to realise you are shagging another man? The true devastation will be the realisation that you chose to betray him. Continued to betray him KNOWING it would upset (kill) him. Lying kills the marriage. Trickle truth kills your marriage. Being a coward kills your marriage. You overstepping the line killed your marriage, all you are doing by telling him is letting him in on the fact you chose to destroy your marriage and hide it from him.
Every time you hug him and smile you are stabbing him in the back.
Ask yourself - are not telling him because you want to CONTROL the outcome. Once you tell him you lose control of your choices and situation. By telling him he will know you are ‘the bad guy’. Others may find out you are the bad guy. At the moment he still presumably thinks you are honest and loyal. If you end up single you will have to admit to new dates ‘my marriage ended because I cheated’ or you could lie.
Often cheaters want to remain in control of their situation. They don’t want people to know their dark side. They say I don’t want to hurt him (you already are). It’s a bit like if you car was stolen today but you are on holiday and don’t find out for a month. The damage has already been done. Not knowing doesn’t mean the theft hasn’t happened.
At the moment you are denying him consent and agency and you are choosing to lie. This is abusive behaviour. You are putting him at risk of STDs and PTSD (your affair partner may have others on the go).
You are very much in cheating mode and sadly cheaters are not the prize. Your husband is in the same marriage (good or bad) and he is presumably choosing not to cheat. He is staying true to his word. His word presumably means something. He is the prize here. You feel like a prize with two men wanting you but only your faithful husband is the prize.
Why were the ego kibbles worth it? You chose kibbles and smoke up the bum over your own integrity and honesty. Why?
Is this really who you are choosing to be?