GF's troubled past impacting us?

I have been with my girlfriend for about 18 months now. I'm 33, she's 31. We have so much in common, similar views and ambitions, and seem to be perfect for one another. I'm just not convinced she's at "hot" for me.
About 9 months ago, I learned she'd been molested by a family member for about 10 years of her childhood and teen years. We discussed how this affected her lack of desire for sex. It bothered me, both that this happened to her but also that it meant she might not ever have a normally functioning libido. I should add that things were amazing until she told me she loved me, after about 3 months of dating. Once that was out in the open and our relationship was "secure", it was like a switch. She admitted later to using sex to keep a guy around. I suppose this should have been a red flag.
Very recently, I learned she had spent most of her 20s being extremely promiscuous. This image isn't even compatible with the woman I know and love now. She has essentially slept with every straight male friend she's ever had, has had many FBs and FWBs (you can look those acronyms up), many at the same time, and a couple of what I'd consider dangerous random encounters. She has been tested and is clean. This I know. She has also been raped several times (date rape, as it was described, but raped nonetheless).
There was therapy of course, and she says she's over it, the past is the past, and it has NO bearing on our relationship. But it seems this behavior continued up until only a few years ago, until her first long-term relationship. When that ended, it was followed by two more sex-only relationships.
Then we come to me.
We met a few years ago and went on two dates, right after she'd broken up with her long-term BF. She dropped me because she just wasn't attracted. A year or so later, we reconnected. I was living out of state. We began emailing and chatting. It seemed we were really hitting it off. When the opportunity arose to return, I took it, and we went out on our first date almost immediately. We'd had sex within a week. It's been 18 months.
So now you have the back story.
I'm dealing with the knowledge of her promiscuity. It's very hard to think she has slept with five times as many people as me. What's harder is the feeling of not being desired. I feel like I am protecting her, that I'm a security blanket. I'm a "nice guy". She loves to cuddle, with me spooning her. But she will not initiate anything beyond that, and usually finds an excuse to not have sex, make out, or anything more physically intimate if I initiate. She will on occasion, maybe a couple of times a month. Right now we're going on three weeks. Just this morning, laying in bed, I began touching and kissing her, and she suddenly began saying she had to get up, it was time to get up, and she leapt out of bed. This seems to happen a lot.
She's made comments regarding ex boyfriends, the type of guys she "used to be attracted to", how I'm so good for her, sort of like "medicine"... She says she loves me. She wants to marry me and have kids with me. On the one had I do feel like we're perfect for one another. I admit I have my own weird hangups and issues.
But I basically do feel like I'm "medicine". That she's with me because I'm safe and thoughtful and take care of her, and make her feel good about herself and her past. I treat her like a princess. I feel needed, but not wanted. I don't know if she's so damaged that she cannot ever truly desire sex or physical intimacy with anyone (within a relationship, I mean, as she said the last year of her previous relationship was essentially sexless - she thinks he's secretly gay, I think he was going elsewhere), or if she's simply not attracted to me in that way. She only ever wants to cuddle, to spoon, with me bihind holding her. When I ask or try to broach the subject, she gets hurt and offended and tells me she loves me and wants to spend the rest of her life with me. I don't have the heart (maybe the guts) to say that I just cannot remain in a relationship where I am not desired. Not wanted. It's killing me because I love her and I want US to be happy.
I don't know what to do. I consider the possibility my personal insecurities are the real problem, and I am seeking therapy, that my knowledge of her past causes me to treat her too gently and not assert my physical needs. But I can't escape the knowledge that she was once extremely sexually motivated, and that the first couple of months were amazing. I know passion is a fire that slowly burns down, but it shouldn't be a switch.
What should I do?