Opinions on ring?

My boyfriend asked me to pick out a few rings I like because he needs ideas. He didn’t give me a price limit but I told him I didn’t want to spend a lot of money on a diamond. I’d rather spend it on a nice honeymoon or something. Plus I don’t want unethical diamonds. What matters to me is what it stands for and that he loves me. So I picked this one out,because it has special symbolism with the butterfly and infinity symbols, but when he told his sister (they’re really close in age and best friends) what he was getting me she called him a cheap ass. I explained to her why I wanted this particular ring set but she won’t stop pestering him to just buy a real diamond without me knowing. I don’t appreciate it at all, and it’s making me feel a little insecure about my choice. Is there something wrong with these rings?