Threesome advice

I’m dying to be with a woman and my husband obviously would love it as well. He says he would love to just watch. I also know he’d love to join. When I’m super horny I think I’d be cool with him joining but I’m not sure. I’m afraid I’d be devastated and wouldn’t be able to get over it. I don’t want to ruin my marriage but I’m afraid me not doing anything will be a huge turnoff. I feel like he needs more to really obtain complete sexual satisfaction.