Betta Fish: Is it time to let go?

I made a post here a bit over a year ago about my betta, Marble, that had developed a tumor and at what point would be best to let go of him. He ended up passing naturally a few weeks later & a few months after I moved back home I decided I was ready to get a new buddy. Being the idiot I am I ended up unintentionally getting the same species (I’m pretty sure) which obviously came with the same genetic issues that my last betta had. While Marble took a few years before he started growing his tumor and suffering from it, Quarts (current fish) started growing his only a few months after I got him. His tumors are even worse than Marble’s were and cover a large portion of his head & some parts of his body. One of his eyes is completely covered and he can’t see out of it, while the other is half shadowed by this gigantic tumor on his head.

I was pretty devastated when it first started and I still feel really guilty. Sometimes I feel like maybe I’m doing something wrong and thats why they keep ending up like this, but I was told that this is just genetic unluckiness (unless I’m wrong and I really am just terrible at this). All of this to say that in the past few weeks, Quarts has started to slow down and spend a lot more time laying in his sleep spots instead of swimming around. He still comes out for food and I’ve tried to make it more comfortable for him (I added a leaf hammock next to the heater that he’s been using to prop himself up close to the surface) and I haven’t noticed any pineconing, but I can tell that his quality of life is getting worse. I guess I’m just looking to see if other people think it’s time for me to let him go & what the best method would be to go about that.