Why is it so easy to look back on the past so fondly and dread the future so much?

My life is good, don't get me wrong. I have so many great friends, countless stories, a good career academically and professionally, I don't have many regrets. There isn't much I could really ask for, mentally I'm struggling but it's by no means the worst I've ever been, overall I feel pretty solid. I just feel like I look back at the past and just wish I could go back, feel the way I did back then, remake some of those memories one last time. There's a couple select months that I wish I could relive again, even though there was some really awful times mixed in there I had the best of times. 2022 I did it all, literally everything and life was beautiful. There were many times I dreaded waking up, there was a lot of rough times involving relationships in my life that I still struggle with. Even though all of that happened, it was still worth it, I would do it all again. So many amazing memories with the people I love, it was awesome. It's hard to understand why I can look back and love that part of my life so much and be so terrified of the future. Maybe it's easy to understand I just can't wrap my mind around it. I worry too much about everything, I think just being so far from my friends is pushing me into a slight depression. I worry that my friends don't care and that I'm losing the relationships with the people I care most about. I know it's not true, I hope anyway, but it just feels like no one really cares anymore sometimes. Not everybody obviously, and I know I'm a softie when it comes to this kind of stuff. But like I call people or try to talk with people and a lot of the time they just don't call back, and that really sucks. I wish people would call and just see how people were a lot more often, I try to call people often but sometimes I forget so I know I'm not perfect either. A good example is one of my friends that just moved away, and I know he's going through it right now trying to adjust to a new place, but I see him talking with his girlfriend all the time and he never really bothers calling me anymore. Or he'll pick up and say he's busy and not call back, sometimes he does but not often. I feel like our conversations hardly mean anything anymore, and that he's just talking to me out of pity, I feel like a lot of people just talk to me out of pity. I don't know if that's the case, I don't think so but it feels like that sometimes that people just don't care anymore. I just don't want to be a nuisance to anyone, I know I'm bothersome sometimes because I call too much or text people a lot, I just care about people and want to stay in touch you know. I love everybody, even the people who've really hurt me I still care about so deeply. I'm hoping I feel better when I get back home, I just want to see my friends again so bad.