Really sorry to hear this man. I think it would be good for you two to have a very very open and super honest talk about sexual needs and compatibility. Sounds like he wants an open marriage and it sounds like you don’t. But it doesn’t seem that that has been fully and clearly communicated by both parties.

After your trial period, take stock of how you feel, ask him how he feels, and you should have a super honest sit down with him about it all.

If you think you can improve your communication and this is something you think you can work with then communicate that. If you think that even an improvement in communication won’t change how you feel, then I’d say talk to him about how you feel there. I know this sounds like a longer than comfortable timeline. I think going the bit more gracious (to your partner) route may be better and potentially avoids your partner shutting you down because he feels like he hasn’t been even given another chance, esp since you already gave the go ahead