As long as she is focusing on you 'being controlling' (I'm not saying you are, I'm using this loosely), she is not going to see him for who he is.
That said, if she's 18, 'talking back' has to be treated differently at this age than you treated it when she was 12. You grounded an 18 year old, college-aged person? I mean, you aren't giving her any reason to stay, you know? How do you respond when she does this? Is it a parent/child dynamic, or are you making an effort to treat her more like the mature adult you want her to be?
I guess what I'm wondering is, in such a tenuous situation with the boyfriend, did you leave room for her to come back? I'm not talking about physical room, but emotional room? If it were me, I'd really try to rebuild the bridge. If she complained about the boyfriend, I'd say "I don't know if I'm the person who should give you advice about this, but I'll be happy to help you find a counselor. I think they could see your perspective better than I can right now." In this way, all those red flags and warning signs would be pointed out by a non-invested, neutral third party.
My sister took off when she was young and it was heartbreaking. Then again, my mom only upped the ante and made it really hard for her to feel emotionally safe to return. If we want them to make adult decisions, we have to start treating them like adults to a degree. In my sister's case, I think this contributed in part to some 'later down the line' bad decisions which were a direct consequence of not having the support she needed earlier. Kids find ways to get their needs met, even if they aren't the healthiest ways. Try to find a way to give her some space, offer support (counseling, not even for you two, just for her, you can and likely should go on your own or with your husband as well, to learn how to renegotiate boundaries now that she's older) and find a way to let her be able to see her own situation without judgment from you.