I don't really have alot of advice on how to get over the feelings. I had them too. Then they were gone over time the more secure I felt that my husband was ok and happy about my new relationship and I saw how much a friendsip with my gf was bringing into his life. Then they occasionally resurfaced.
I wanted to say that, in a weird way, it's sweet you feel weird and guilty despite the women being ok with the situation. To me, it shows you really care and love them and want everyone involved to feel as equal and happy as you do. Just don't let the guilt overwhelm you. As long as communication is kept open and you're not forcing anything they don't want you have nothing real to be guilty about.
I'd rather be hated for who I am than loved for who I am not.