So confused!

I really don’t know where to begin really. So I’ll just type what comes to mind and hopefully you will kind of understand lol. Sorry if it’s long in advance. Here it goes: My little (half) brother is getting married on the 22nd of this month. I haven’t seen him in almost 3 years. We’ve had I guess you could say a rollercoaster of a relationship. We use to be so incredibly close when he was younger. We are about 9/10 years apart. I honestly don’t know when our relationship started to fall apart. I suffer from extreme anxiety and depression so when things get tough or I have the choice, I will stay away or keep to myself. So needless to say I never really came around cause I’ve always felt unwanted or loved plus his mom treated me just as such. So as I got older I just didn’t feel the need to be around. I loved my dad to death, he was my favorite but I felt I was always a burden and felt that my brother and everyone else came first before me. My dad died 6 1/2 years ago. I wasn’t around. My anxiety and guilt and multiple other feelings became overwhelming that I chose to stay away and just kept saying oh I’ll visit tomorrow or I’ll go on this day. If any situation could be avoided, I easily avoided it. So like with anything tomorrow is ever promised. I’ve been riddled with guilt and what ifs ever since. I have no closure. I have so much anger and resentment towards someone who isn’t even here. It come and goes in waves. My step mom included me in things after he died which I never understood. She was downright awful to me. But I guess a part of her wanted me around cause I was a part of him. And I talked to her and was around cause I guess I felt I still needed that acceptance from her. I’ve been always excluded on that side of the family whether intentionally or not. My brother doesn’t seem to care whether or not I’m around. At least that’s how I feel. My step mom passed away in 2018. I wasn’t there for my brother because I felt I didn’t belong or didn’t need to be there. I cared about her of course but still she had a hand in why I feel the way i feel when it comes to being unwanted or loved. True I could change that and be the one to reach out and what not but I feel it’s so hardwired into my brain that I don’t actually think anyone cares or wants me around. It’s just a bunch of mixed emotions. I don’t know if I got side tracked of what I was trying to get at but if I did I’m sorry lol. Basically he’s getting married, he invited me. I’ve been changing my mind back and forth whether or not to attend. I haven’t seen him or any of that side of the family in 3 years. With my anxiety I feel it will be overwhelming. Questions go through my mind constantly if does he care if I’m there? Do any of these people care? I’m basically a stranger. My step brothers and their wives and children are going to be a part of the wedding while me and my daughter are just guests. And I’m okay with that because we’ve been estranged for some time and I don’t expect him to include me just cause we are related. I just know that I’m going to feel hurt regardless. I feel like I don’t belong. But then I’m like it would be what my dad would of wanted. This has been an emotional trigger for the last couple of months because I honestly don’t know what to do. No one knows what to tell me. I have no one to talk to. I don’t speak to any of my dads family or my step moms. My mom just tells me flat out, don’t go because of how awful they have been to me in the past. I just wish I could speak to my dad 😔 once again sorry for the long read. Lot of stuff on my mind with no outlet. What do you think I should do?