I'm concerned that she is spending so much time with a much younger boy, so there's probably a significant maturity difference (unless he's exceptionally mature for his age). And of course I'm concerned about supervision - and I truly hope you have had multiple, in-depth conversations with her about sex, pregnancy, and STIs.
I'm not concerned that she's pulling away from you - although I AM concerned that your emotional health is so wrapped up in her time. Read Gidget's answer - again. Your daughter SHOULD be pulling away as she gets ready to leave the nest. Her increased independence is what you should want to see, as a sign of her healthy individual sense of self and her ability to function on her own. Once she goes to college, you don't want her to be a mess because she's away from her mom - you want her strong, resilient, and competent. It's really misguided to put her in the position of having to care for your emotional health. Think of the mama bird who literally kicks her offspring out of the nest - it's part of good parenting. In fact, her desire to be with his family (church, Christmas, etc.) may be precisely because you are coming off to her as needy and clingy.
Your daughter may be looking for companionship from a male, since she has no father in her life. She may also be choosing a younger boy, knowing that she will be leaving him to go to college, where their interests will diverge intensely. As long as your daughter doesn't get pregnant, and unless there's more than you have written here, I doubt this relationship will last into next year. Since he's young, it may be easy for her to manage this relationship and be the stronger, dominant one. That could be a good thing, a good coping skill.
I disagree that she has no life beyond this boy - she has her studies, her activities and her job, and apparently none of them are suffering. The only thing she's really giving up is you - and I know that hurts. But it has to be. And again, it may be because you are trying too hard, trying to take them both to dinner and for ice cream, to pal around as a threesome. She's trying to move beyond that. It may also be her defense mechanism against missing you next year.
Please let her know how proud you are of her and all that she has accomplished, and do continue to invite the boy for dinner now and then, being the most welcoming and amusing mom you can be. Don't criticize her for not doing things with other friends - she's going to be leaving them, and they're going to be leaving her, soon enough.
Please stop with terms like "discarded ragdoll" and so on. I guarantee you that your daughter may trot off on the college campus with a wave and a "Go home already, Mom" attitude, but she WILL miss you and the comforts of home. While I think you are deluding yourself that she "tells you everything," I believe you are setting things up so she tells you nothing. How about a compromise? Let her come to you for counsel and to share some things, but stop insisting that you share everything. It's not normal for a young woman to be best friends with her mother, and you are wrong to encourage that. She must be able to survive on her own, and so must you. Please develop other interests and stop putting so much emphasis on enforcing every rule you can think of, lest you drive her away. Start being more confident in what you have already done to nurture a smart, active, hardworking kid, and start making the break now.