Ugh - my husband has a daughter like that, thug boyfriend and disappearing act, and all that. I feel your pain.
I don't know if you gave her too many material things and too much structure/discipline, or if her father gave her way too little, or if this all came as a complete surprise with not clues at all. If you are completely shocked and it's not because you and your husband weren't paying attention, then your daughter is a very accomplished liar. I'm sorry, but no high school senior gets away with so much unless you weren't checking up on her on the big stuff.
But then again, some kids just flip a switch when they turn 18, and get this idea that they are invincible and totally independent. They forget that they really aren't, because the parents are paying the cell phone bill and the car & insurance, medical coverage, spending money, and the things you list like the prom dress.
If the boyfriend isn't going to the same college, I do think your best bet is to get her off to college. That leaves the next 2 months in play. So I would cut off her cell phone for now, and maybe pull the plates/insurance on her car. If she disappeared and lied, she's not responsible enough to have electronics and machinery. But that's if YOU pay all of this and her father doesn't, and if he will cooperate with you. I think you give in on the curfew, but insist on some communication from her and some honesty.
Once you get her attention, you sit down and tell her that, if she's totally independent and living on her own, then she can pay her own way through college and get herself a loan. Federal loans are not hard to get, and you absolutely REFUSE to put this in your name vs. hers. She can pay it back with a low interest rate after she graduates.
But you have to be concerned with her behavior because, if she doesn't get her butt to class and if she blows off the homework, she will lose her scholarship. If you want to offer some sort of help after the fact - if she gets decent grades (not all As but enough to stay on the team), then it can be a reward IF she complies.
You have to finish crying, and although you can keep praying, there's an expression that we have to "pray with our feet" - that is, we don't pray passively only, but we pray for guidance and strength to take action. God isn't going to take care of this for you or for her. God's going to give you some answers, perhaps from your friends here on Mamapedia, and help you open your eyes and ears to choose a good option.
You MUST realize that you have to have a backbone, and that you still have a ton of control here. You can't nag her into coming home by 11 or any of that, but you can certainly step back and stop providing for someone who thinks she's such a grown-up. Your ex has to step up, but maybe he won't. It sounds like he's giving up after a short time.
So you can start by packing up her things and delivering them to her father's house - don't ask permission, just do it. Put them in a safe place like his garage or the back porch, and inform him and her that they are coming. Make it about "convenience" for her, not "I'm kicking you out." Transfer the phone into her name, give her the name of the car insurance agent if applicable, and make it a "gift" for her graduation and her adulthood.
Make it clear that adults don't whine, so you aren't going to listen to any tantrums or sense of entitlement. And tell her boss that you aren't taking calls for her, he needs to contact her directly. Tell your ex you aren't listening to his complaints if you don't have an agreed-upon parenting plan between the 2 of you.
Get counseling, with or without her dad, asap. Please put aside the argument that you and your husband have given her X Y and Z - no teen wants to hear that. This is not about her gratitude to you or what she owes you - and don't tell her who to date. You DO have the right to insist on truth, whereabouts, and some sharing of expenses if she's such a big grown up. But you aren't taking on $5000 in debt (and did you account for books and spending money and activity fees and "extras"???) for someone who isn't trustworthy.