No I am not calling him a beast. The word Bull as in reference to another man not your husband. Putting himself inside you while having sex then cumming inside you. Your husband would be called a Cuck since he allows this. Then if he watches it would be called a Cuckold.
Strike two Bruno. You need to study the habits of the cuckold bird. It is clear no sharing is involved nor is the "host" party aware. I agree if she were doing this behind my back, without my knowledge then indeed the term might apply. Our sharing is with my knowledge and consent, always threesome, and the term does not fit. Check out the term "Candalism", particularly as used in seeking.com/glossary/polyamory-jargon/candaulism. Now that one does apply.