Hiya @Sophia0Martinez welcome to the community.
I hear you and so much, this is quite relatable actually hehe and so I deeply understand how hard it is to set boundaries without feeling like we are doing something "bad" or treating someone "less-nicely" (lol even during the times we might be the ones being treated poorly~ *inserts a clown face for self*).
While feeling guilty when saying "no" to someone or the times we are prioritising ourselves is a common experience for many many people and you're definitely not alone in it; currently what matters here is *you* and your feelings, so I'd like to hear more on what makes you feel guilty when you tell someone a "no" or setting boundaries?
And what thoughts usually occupy your brain when you're trying to prioritise your wellbeing?
What I personally have found to be of some help in not letting myself feel "guilty", is questioning the root of where the guilt stems from; often times, our conditioning and past experiences where we are made to feel like our feelings do not matter as much, or that we've to brave up and be the one accommodating others' needs even if in reality it is that they don't even acknowledge our own.
So it's superrr important to recognize yourself as an individual, and an individual with needs, wants, tolerance and values.
Got to step up and value ourselves more when others do not, specially when others do not.
To remind ourselves that we are hooman too with feelings and emotions, and that we do deserve respect and consideration.
To remember that boundaries aren't for distancing from people entirely or to make someone feel "restricted" in their access to us, but to boundaries as a way of self-care, a way to be kind to self recognizing and respecting our own needs and wants while acknowledging and understanding the other person's as well.
Often times, when aren't able to say no to something, we may reluctantly agree, but it does affect and take a toll, because our mind and body do have a way to remember when its disrespected in someway.
Setting boundaries not to make people feel bad or change the dynamics of the bond, but to strengthen the bond by holding space for honesty, authenticity, trust and communication.
What I've found helpful here is to shift the perspective on how I view myself, how the people around view me, the concept of boundaries and self-esteem.
This got a bit long, but at last, I just want to reiterate that you're doing sooo amazing by recognizing your emotional needs and being willing to work on setting boundaries for a healthier relationship with yourself and others. It takes courage to stand up for ourselves, when we've been left questioning if we deserve it, but hey, you are trying and it counts, so so proud of you. 💛
Also, here's a guide on boundaries, if you haven't checked out already- https://www.7cups.com/boundaries/
And yes of course, would like to know more about your thoughts, so feel free to share! 💛