Losing a pet is really difficult. I lost my dog about six months ago, and I had a really hard time with it, mostly because not having her there was way too strange. Honestly, not having her around still feels off- we had her for 10-11 years, but it would've felt the same if we only had her for one or two. Don't blame yourself, feel free to be miserable for a little bit, then keep going. And at least you'll have good memories of your guinea pig. Sorry about Scuzzy (cute name, btw). It sounds like he lived quite a long time for a guinea, and it looks like he had a decent last year.
Don't blame yourself, you did what you could to make him happy and comfortable. Guinea pig's expected life span is usually somewhere around 7 to 10 years anyway, so he was pretty old when you got him. I know loosing a loved one is hard, I've been there so many times with all the animals me and my family has had in the past.
I'll add that for at least a month after my cat died I kept hearing her and seeing her in the corner of my eye. Sometimes we are so used to them being there and being a constant in our lives that we forget they aren't there anymore.
5 years ago i went to chicago for my brother's graduation and when i returned home i found my elderly cat lying in a clothes pile crying. She was dehydrated and hadn't eaten anything. The caretaker (neighbor) said "She wasn't eating her food and I didn't know what to do". I tried to give her water and revive her, but she died in my arms. That was sad
But, she was 16, she had a good, long life.
My dog is now 15 year old, she doesn't have much time left, but she's also had a good life, she was abused when she was little and we adopted her at ~1 year old
No matter if a life is long or short, you did everything you could to keep Scuzzy happy, and you did, so do not feel bad over his death, just because an average is x years doesn't mean they will make it to that, or they can live well beyond it.
Cherish the time you had with your friend, and it's okay to mourn. People who don't have pets don't understand that it's like losing a family member.
I have a fat cat that rarely leaves the yard. She is under a bush or on the porch. Then she was gone. I looked all over for her and even walked up and down the street to see if she had been run over but she was no where to be found. I really missed her. She was gone for like 3 days. But last night my room mate said she was back. I went a gave her a big hug. Don't know where she was but she is back, and I know if something had happened to her I would be really sad. Sorry for your loss.
I'm so sorry I know how you feel. My rabbit died a year ago, and I still miss her so bad. I was in the same situation where I didn't want her to die of illness. I'd been away on holiday just before she died, too I felt like I'd failed her.
Just remember that it wasn't your fault. You did what you could for him, and there's no way that you let him down.
A couple of things that help me is that I wrote in a diary, my fave things about her, memories of her and how I felt. Also, drawing her helps sometimes. Idk what you think of homeopathy, but imo my homeopath did help me out.
7 years is a good age for a g-pig, and given that he was neglected before you got him, it was an old age to reach. You did well.
I cry hard, when I lose a pet. I've had g-pigs most of my life, and they truly are wonderful pets.
My best advice to you, is to get two new ones. (They need each other, as they're pack animals.) If you can wranglet it, get a female and a snipped male - they snip at shelters, I believe, and sell them at a little higher cost. Get two that don't look like Scuzzy at all, so you won't constantly compare and feel sad. If yopu get two, you'll get to see al that fun interaction stuff. Talking, playing, arguing, and getting each other riled up at feeding times, and so much more.
It's OK to love again, and it doesn't mean you're somehow letting Scuzzy down.
If you do decide to get a couple of shelter pigs, know that they might be damaged from earlier, but also know that you would be a wonderful forever-home for them.