If your new love's husband is saying he's okay with the situation, but you're getting the feeling he's not, more communication is called for. Talk with him. Encourage her to talk with him. The four of you get together if that's appropriate. But talk it out. With love, respect and compassion for everyone concerned. Find out what he's feeling, what he needs in order to truly be okay, and together make a plan to be sure his needs are met.
One challenge that is unique to polyamory is handling NRE (New Relationship Energy) while maintaining a more mature relationship. It sometimes happens that the two new lovers are so caught up in all the delicious feelings of new love that they neglect their established relationships. This is completely understandable, but it can be devastating to the the neglected partner.
Take steps to make sure this is not the case for y'all. As her "old relationship" he may be having a hard time seeing his wife overcome with NRE with you. He may feel left out, or envious, or feel that his needs are now less important in his wife's eyes than the needs of the new relationship. (Of course I can't say what he's know what he's feeling, and neither can you at this point; that's why more communication is needed.) If any of these is the case, you need to make a plan with your new love to make sure his needs are met.