You have worked hard and done well. Nobody is saying that you’re not a high-achieving and accomplished student. The issue is that you’re aiming for schools among the top 50 in the nation, where most applicants are rejected, and where most applicants are highly qualified just like you. The small advantages you have, like legacy status, probably serve at best to counterbalance the disadvantage of being a local applicant - colleges want a mix of students from all over, so it’s always harder to get into your home-town elites. On top of all that it’s not clear that it’s financially feasible for you to attend an expensive private university.
I’m sorry that there’s been a level of harshness on this thread that makes painful feedback even harder to hear. I don’t know how whether your financial aid prospects would have been favorable even before your mom got married (because unfortunately, just telling schools that your dad doesn’t support you is not enough to exclude his financial info from their calculations), but there certainly can be negative unintended consequences in situations like this. I understand that your frustration doesn’t mean that you begrudge your mom her happiness, but just that you’re upset that she didn’t think through how this would affect you. People here have gotten upset at how you’ve expressed that frustration but I feel like we should cut you a break on this front - you’re dealing with a lot of upsetting adjustments in expectations, all at the same time.
I agree with what others are saying, that you have fine options within the public university system in MA. If UMass Amherst is your goal, you can certainly get there, possibly as a freshman, and certainly as a transfer from either a different UMass campus or a CC. As I said before, if you want to go all-in with a studio-based architectural design program, you could commute to MassArts.
What state does your dad live in? If you want to use your gap year to establish residency in a different state, it would need to be either the state where your dad lives (if it’s different) or one of the rare states that allow students under 24 to establish residency independently. (Utah and possibly Missouri.) I’m not sure whether it’s helpful to discuss moving far from home on your own, since it sounds like you’re dealing with a lot in terms of your mental health right now and need a support system. But if your home life is part of the problem, relocating could be a possibility. The other way to decouple your state of residency from your parents and secure additional funding for college is military service. But it doesn’t exactly sound as if basic training is what you need physically and emotionally right now. At any rate, Massachusetts is a pretty great state to be in, from a higher ed standpoint. You could be in much worse shape in many other states, both in terms of the quality and variety of opportunities available, and in terms of affordability and state-level financial aid.
If you really want to explore the possibility of a private university in the BC genre, I would suggest you take a closer look at Holy Cross in Worcester. They have an architectural studies program https://www.holycross.edu/academics/programs/visual-arts/architectural-studies and their track team is one of the lower-ranked programs in the Patriot League, so perhaps a good target if you’re borderline for D1. And they meet full documented need. So run their NPC and see how it looks. It’s an excellent school and your stats are only a hair below their median. They have EDII, which would double your chances of acceptance (and would be binding only if your financial aid offer met the expectations set by the NPC). You could still defer for a year once accepted, and take your planned gap year.
Hang in there and don’t feel like you have to figure everything out at once. Take the time to work through everything you need to. There will be a path forward.