How would you handle a situation concerning your husband & another woman that is "just a friend"?

My husband is a great, popular guy that likes to help people. I am his #1 supporter. We have had a great marriage, no doubt to his faithfulness to myself and our family. I have issues, due to my past and my adulterous father, I have grown to be weary of pretty much all females. 7 months ago; I started to feel lonely due to the busy lifestyle, having always spent a lot of time with him during our marriage. He invited me to get involved with the chat communities that he was in and hang out with him while he worked. I did this and found that he had befriended a lot of people; men and women alike. I expressed my feelings about him and other online women and he understood. A month later he did it anyway. She is married, with a family and he thinks that this is safe. He told me of her and I'm not thinking that it's serious because of our discussion. Wrong, 2 months ago I find out that they talk to one another every weekday for about 3 hours on IM and she sends him drawings she calls "gifts". He presses me to become her friend and has invited her to hang out with us on or vac/anniversary trip. I am skeptical of her intentions, because "why does she spend so much time on my husband". He has made statements about missing her and noticing when she isn't on IM because "she is half his daily conversation", but she is “just a friend”. We meet on or trip; she happens to be identical to me, with my demeanor when I was about 25 even though she is my age. Everything that he fell in love with 12 years ago. She hangs out with us all weekend and I see complete adoration in her actions for my husband. She bought him a gift too and “do I mind if she mails it to him”. I mention this to him and he is OK with it but, this was/is unacceptable to me; I tell her she is crossing a line and it makes me feel uncomfortable, she backs down and says forget that she even mentioned it. After she left, I express my concern for her attachment to him and he denied noticing anything. We return from the trip unsettled, I continue normal relations with her as did he. A week later, my husband comes home and mentions a "really weird" video she sent him. I waited all weekend to ask her for the link and she produced it for me to watch. I did, only to see that it was Die Antwoord – Evil Boy, (watch it). Totally appalled, and feeling utterly disrespected, I didn't know what to say. She freaked out thinking that I was mad at her (she was right), (she had guilty conscience, knowing that it was a totally inappropriate video to send to my husband). I handled it gingerly, so as to not embarr my husband, but it didn't sit well. I asked him what they talk about that would make her feel comfortable to send him something like that and he said that it was just a goofy video and defended her. A week ped by and I overheard a conversation between my husband and a few friends from the online community; there were some ual insinuations from the friend and it was the final straw, on top of everything I didn't want any rumors. No matter what I thought about this women, he never listened to me he'd just shake his head and call me crazy. I begged him to end contact. After crying everyday and having him choose the feelings of another woman over my own for 2 months, he decided that he would not be talking to her anymore over IM, "not because he didn't want to, but because I couldn't handle it", my complaining “wasn't worth it”. Under the bus I go, right. Later that evening, the two of them happen to be on another chat site that I am on as well and she posts a link to a song; songs that he always listens to (except this time he didn't), I did though; Radiohead: Fake Plastic Trees, listen to it, you'll understand. I recognize her message and let her know and she denies it of course, because "Why would she do that"? One thing leads to another and my husband reluctantly promises to never talk to her again. I don't like being this way, I want him to help people and be happy, but not at the expense of my sanity. He can help people without creating any issues at home. He chose to let me suffer, so that he could keep her happy for months; truly suffer. He's sad now, because "he **** on her", but there is no remorse for what he did to me. I honestly don't know how to get my feelings for him back to the way they used to be, I feel cheated, hollow & crushed. Like I don't have the place next to him anymore; like I am easily replaced. Even though he says that he could not live without me and she was just a friend. I feel like he resents me for separating them. He has NO idea what damage he has done to me, all the fears that I have worked so hard to get rid of from my childhood are right back and agonizing. I need advice, PLEASE; Did I do the right thing? How do I get through this?