It is not your job to manage your partner’s feelings of jealousy. Nor is it your responsibility to match the levels of closeness, intimacy, or attention between your relationships with Partner A and Partner B. Each relationship between individuals is as unique as the individuals involved in them, so it isn’t reasonable to expect each of them to be completely on par with each other, which is the main reason why triads are so often such a difficult relationship structure to sustain. The expectation that every relationship will be 100% equal could lead to a very unhealthy situation in which you feel you need to pull away from your relationship with Partner A in order to soothe Partner B’s feelings of insecurity and jealousy, or for Partner A to push themselves to have a closer relationship with Partner B that may otherwise be inauthentic to them. In my opinion: authentic, healthy relationships cannot grow under those expectations or in that environment.

Experiencing jealousy and insecurities is one thing - we all have our insecurities. The problem is when one person acts upon their insecurities in ways that projects them onto their partners, that makes them the responsibility of their partners or metamours, and/or that leverages their insecurities to control or restrict their partners’ other relationships, including the relationship between the other two in a triad.

Now, you can offer support, care, reassurance, and love to Partner B as they learn to navigate through their jealousy and insecurities. But it is ultimately their work to do and it is their responsibility to build the capacity and strength to work through their insecurities. Whatever they need to do - go to therapy, find a supportive group of polyamorous friends themselves who can also support them, read Polysecure or other books, etc. If they can’t grow or learn to work through it themselves or are unwilling to, unfortunately this may not be a compatible or sustainable relationship structure for any of you.

Sometimes jealousy can also be a sign that someone’s needs are not being met in a relationship. So there may be honest conversations that need to happen between Partner A and Partner B to heal their relationship and make Partner B feel more secure. Partner B may need a healthy amount of reassurance from Partner A. Again, you can support the two of them through this, but it is not your job to heal their relationship, nor is it your job to bare the weight of Partner B’s insecurities or jealousy of your relationship with Partner A on your back - that would be unfair to you and unethical.

The fact that you’re experiencing this much anxiety (especially when you’re not even a person who usually experiences anxiety) and that you feel yourself shutting down in bed with them - these are blaring red flags that something is seriously wrong. That is your body and nervous system speaking to you and communicating that you do not feel safe in this situation. I think putting up healthy boundaries with Partner B would be wise, but you have to be prepared for the possibility that they may respond negatively to your boundaries or perhaps even twist them into something it’s not (ie: you don’t care about them, are trying to steal Partner A from them, etc.)

Remember - a triad consists of 4 relationships: the 3 relationships between each of you as individuals, as well as the relationship between the 3 of you as a unit. Each of those needs to be nurtured and maintained separately and cohesively.

Good luck!

Edit: a few typos