People would absolutely miss you if you were gone. We would, your friends would, your trainer and therapist would, I'm sure your clients would, your family would too, even if they aren't supportive like you want. You are going through a ton of sh*t right now, and it's completely understandable to feel such a roller coaster is emotions. But you should never feel like you don't influence this world and the people around you.
As for your mom and step dad, honestly it sounds like you need strong boundaries with them. They need to understand exactly why the things they do or don't say and do are so hurtful to you. If they can't support you, or at least respect you enough to reach out for more than selfish wants, then they don't deserve the pleasure of your company. It sounds like you have a long history of being brought up to sacrifice yourself for others, while being surrounded be people who wouldn't do the same for you.
I'm sure this won't surprise you since I've pointed it out on several other posts, but the part about leaving to support your mom while she was suicidal really stuck out to me. It's admirable to care for your family, but you cannot be someone's suicide watch. You have your own needs to meet. Caring for your mother is not your full time job, particularly when she won't provide you that same level of care.
You'll get through this one day at a time. You should re read your posts about not thinking you'd make it past 3 days, and now you've made it 3 weeks. You're already healing, and you'll keep doing so as the weeks go on.