When people feel hurt, genuinely, it is something that happens in the moment. You deal with it, find a way to heal, and make all efforts to move on. But it sounds like your husband has not been willing to forgive and let go of the hurt. He is holding onto it and using it against himself and you. As long as he can say he is hurt, he feels justified in playing victim, being stubborn, and/or demanding some form of reparation from you. It is often difficult to let go of our indignation and sense of having been offended when we feel hurt and are wrapped up in blaming someone for that hurt. But the fact is, as long as he refuses to forgive, and hangs on to the idea that he is hurt, there is nothing you can do or say, and nothing your bf does or says, that will ever be enough to make up for it and erase the hurt. He needs to look at that and move on. He is the only one who can help himself not feel hurt, actually. At one point, his hurt feelings may have been an organic reaction that just arose in the moment when things first started, but now he is just indulging in it and choosing to feel hurt. We all do this sometimes.
When you forgive someone, it is basically starting over and saying the slate is clean. You don't keep punishing someone for whatever you associate with the hurt. What your husband is doing is holding it over your head and demanding that you pay for your "crime" by not giving you what you want.
It also appears, from what you stated, that he feels a sense of ownership over you, and your bf is competition trying to oust him from his place as someone who hold possession over you. Instead of going to him with your hand out and asking permission, if I were you, I would assert my autonomy. All couples, whether monogamous or polyamorous, are individuals with autonomy to make their own choices. I would say to him, "Honey, I know this has been hard for you, but I want to have overnight stays with my lover. This is something important to me and if we are going to have a strong foundation in our marriage, you need to deal with your resistance to this. What can we do to make it easier for you? Let's come up with a plan to make this transition, because it is going to happen eventually but I'd rather do it in a way that eases you into it." Something like that.