It sounds to me like you've been able to experience other lovers with better techniques, is all. And now what your husband does just doesn't quite measure up. It's a matter of having more experiences to judge against.
Does your husband know you're not as satisfied with his lovemaking skills as you were before you starting swinging? If he does, his confidence level may be down. Maybe he feels like he has to compete with the others and doesn't feel able to.
I think you need to talk to him, outside of the bedroom, about this matter. Reassure him that you love him. But let him know that your lovemaking isn't as satisfying as it used to be. Ask him if he's bothered by anything.
I wish I could be more helpful, but I wish you all the best. This is one of those things, I feel, that can be worked thru with open, honest communication.
DragonsLair
He is T. I am A.