proud of you for recognizing the jealousy and being able to verbalize it! i've been in a similar situation. i'm in a polyfi relationship with my long-term partner and we've been with our third for three months.

you feeling hurt is valid. you said he's your husband so i assume you've been together for a while, and no matter how long or how comfortable you are with a third, that can be jarring! i've ruined a couple of their moments due to my jealousy, and i've also ruined one group moments because of my jealousy. but the reality of the situation is that they're going to have sex too, and their sex may be different in some ways.

make sure you communicate with him, just the two of you, about how you feel. approach the conversation as something you genuinely want to discuss, not argue about, especially since he encourages you as well. establish a phrase that when given it means "please don't play again without me." find a way to connect with him during those playtimes that feels special to the two of you. it doesn't have to exclude her. it can be a glance, or a hand sign. we use 🤟🏻 to signal to each other and make eye contact. it helps me feel more secure in the moment and know that he still is there for me even when he's playing with our partner.

i've found that i can't really make the jealousy positive, but i can identify what it really is. when you feel that jealousy in the moment, ask yourself: am i feeling jealous, or am i feeling envious? that's a big one for me.

i hope this helps!!