As long as everyone is clean and stays within the circle, it should be fine. That's how my wife has been with our friend who is fixed and only been with his wife. Since she cut him off a few years ago, he is only able to enjoy my wife and gets to cum deep inside her which causes her to flood his cock with her juices. Then feeling their combined cum feels amazing when I slide into her. He and I also have licked her out afterwards. Drives her crazy. She's beginning menopause, so her hormones are all over the place.