You've received a lot of great responses here. I'd like to add a little perspective that may help you along your way.
One of the most difficult things for most WS's is to get themselves out of the self-focused frame of mind that got them into trouble in the first place. After Dday, I wrote my wife letter after letter, pouring my heart out to her, apologizing, telling her how much I loved her and how I wanted the best for her and how I knew we could make it work together, so on and so on. And every time, she basically threw the letter(s) back at me and told me it's still "all about me" and had nothing to do with her. This confused the living shit out of me for the longest time, because I felt that my letters could not have been more caring or compassionate than they already were. I simply didn't understand how "I love you and I will never stop trying to save our marriage" was a bad thing to say. But it was. And it did SO MUCH damage to our relationship that it is hard to even put into words.
I mention this to you because I see in your words many of the same mistakes that I (and frankly, most every WS here) made early on. If you can begin to get a grasp on what it is your BS needs from you in this time, it could save you both a lot of pain and help your reconciliation efforts immeasurably.
Let's take your title as a simple example.
How do I get over the fear of losing him?
This is fair question, and a reasonable fear, to some degree. But it's not a clear point of view. There is no ownership in this statement. There is very little reality in fact. And it lacks compassion for him and his experience. In order to help explain what I mean, consider this sentence:
I drove my car into a wall last night. This morning, I'm worried I may have damaged the car.
Someone else reading that might suggest that you "already did" damage the car. It's not something you need to worry about doing, as you've already done it. The question now is "what are you going to do about it"?
When you say you are worried about losing your husband, it doesn't really reflect the reality that you've already thrown your marriage, your husband included, out the door. In other words, through your own actions, you've already lost him, because you disposed of him. You can't lose what you've already thrown away.
Stop and think of what/how your husband felt when he learned what you did, when he saw those nude photos of you being sent to strange men, when he read you asking about BDSM, when he learned that you were living a double life, one built entirely around the practice of betraying him, lying to him, hiding things from him, and at the same time, giving to other men the very things you were keeping from him. Do you think he thought to himself, "Gosh, I might be losing my wife?". Or did he think, "Holy shit. My wife has left me. She doesn't love me, doesn't even want me, kicked me to the curb like a chump and started offering up her goodies to complete strangers because she can't even conceive of wanting those things with me?"
Marriage is a contract. And marriage is work. And when you break that contract, when you work against it, it means the marriage is OVER. It's like dropping a raw egg on the floor, you can't put it back together again. It makes no sense for you to fear losing your husband when you threw him away in the first place. Understand? Worse yet, from his point of view, your emotions and actions are still very selfish. You didn't say, "I'm worried I did so much damage to my husband that he may never be happy again. I worry that I may be more of a danger to him than a help. I worry that I broke his ability to ever trust anyone ever again. I'm worried that I've hurt him so deeply that he may never fully recover." Now THAT's about HIM, not YOU. It's not about making you feel better about what you did and undo what you broke. It's about caring for someone else's pain unselfishly, with empathy and compassion. He doesn't need your apologies, they don't help. He needs to know you understand what you did and how it affected him, and he needs to know that you understand why you did those things to him. If you don't, then all of his suffering is not only painful, but also meaningless, which is a hundred times worse.
Now, to be clear, it not my intention to make you feel badly about yourself or what you did. I'm a WS too, we all are here, and we all did the same things as you did, and face the same outcomes. My intention is to help you understand what actually happened, because until that happens, you can't really progress.
The things you've written so far (very much like the "all about me" letters I wrote my wife) are still very much all about you. Staying together is an outcome that YOU want. It is what YOU feel would be BEST for HIM. But let's be honest, it's what is best for YOU. If your best friend came to you and told you that her husband was sending dick pics to strange women and asking them to spank him, would you respond to her, "Hey, he sounds like a peach and is probably the best thing for you ever, you'd better stay with that prince." No, of course not. You tell her that he's trouble. That he clearly does not love or respect her. That she should consider dumping his ass and finding someone else truly worthy of her. So what if he's really sorry? It didn't bother him enough to not do it this time, so why suddenly believe it will be enough next time?
So I ask the same of you. What about staying with his cheating wife is what you think is best for him? Why should have to do the work of R with you when he did nothing wrong in the first place, how is that a bonus for him? What about you has changed so very much that you could not possibly ever cheat again? If you truly love him and want what is best for him, then how can you possibly suggest that staying in a broken marriage is the best path forward?
These are the things you need to get through your head now. This isn't a loving marriage that is facing a new challenge. This is a destroyed marriage, and the person who destroyed it isn't even fully aware yet of why/how she's so broken and how to go about being a safer partner. Your husband cannot trust you yet because he has no reason to do so. He did so before and look where it got him.
If your goal is to try and save the marriage, then your first step is to figure out your "Why's". Why did you have an affair? And I don't mean, "Because you wanted to". I mean, what in your life allowed you to lower your standards so very much that tossing your own dignity and self-respect out the window (as well as your loving husband and the marriage) right out the window for a cheap thrill? What drove you to become a liar, a betrayer, and to live a double life? Those are not small things! Those are BIG problems! Until you fix yourself, until you understand yourself, then nothing changes. You remain a danger to him and yourself.
Please keep coming back. Infidelity is a shit-show all around, and both the WS and the BS have trauma to get over, work to do, and new paradigms to accept. I am in year 7+ of R with my wife. For the first few years, I did everything wrong, and it caused so much damage. Once I pulled my head out of my ass, got my perspective and my empathy back, it opened up huge doors towards successful R, and you can too. But it starts with the self. Get a good IC, and work with them to determine how and why you are where you are now. It may not save your marriage. But it will save your life.
[This message edited by DaddyDom at 12:33 PM, Wednesday, August 9th]