Good afternoon and thanks for writing JA.
I believe your first step is honestly to set an appointment with a family therapist - not for your daughter - but for you. You will need to sort out the process of individuation that your daughter (and you) is currently experiencing. Some of this behavior is consistent with that process of becoming an adult - and much of it is normal.
However, your reaction (while completely understandable) would likely be considered "enmeshed" by most family therapists. Meaning: it's difficult for you right now to know your own boundaries and your daughter's boundaries. (Example: you shouldn't have to "humble yourself and apologize" to your daughter for expressing yourself (if it was appropriate). As you later stated, you're allowed to set boundaries! By the same token, your reaction to "snooping" (violating her privacy) was one of shame - which is appropriate - and further indication that it's hard for you to respect her boundaries right now.)
By embarking on this process, your daughter will recognize that you're going to someone to sort out some of your issues (you don't need to be specific with her... this is YOUR business, not her's). Your modeling may show her that it's OK for her to talk about what's going on with someone and she *may* choose to go to someone (this family therapist or her own) or she may not. But you will be laying the groundwork to demonstrate, "when I start feeling sad, out-of-control, anxious (etc.) - I go talk with someone." That's a valuable lesson for your daughter to learn, even if from afar.
So: remember when the airline attendants tell you to "put the oxygen mask on yourself before helping your children?" The same thing applies to this situation. You need to find someone to help you sort out your feelings (not just about this incident with the BF, but with the overall process of your daughter growing up and growing away from you) before you can be of any help to her. You may be able to help her when you're in a good place. But right now - I think you're too close and too "enmeshed" to be able to help her <or> you.
I know this isn't probably comfortable or welcome advice, but please consider carefully... I'd be happy to answer other questions or respond to any thoughts you might have. If you'd like me to open this to other experts as well, I'm happy to do so.
Thanks. Best of luck to you and your family.
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