I don't think anyone is saying differently than 'if it works for you good' because it does appear to work no indication that it doesn't. But of course making comments means comments can be made about said comments you've made
On a general sense I don't think a relationship is an factor. I met my husband, while in college though, and while marriage was at least talked about early enough, there was no desire to get engaged before we were both out of college. That was more than 3 1/2 years for my husband before he graduated And we didn't live together until we got married so we had separate apartments the entire time. My sister-in-law just moved into her boyfriend's place at age 28 after nearly 3 years of dating. Just because you have a significant other doesn't mean it's an 'obvious cohabitation' option nor is marriage a thought for all with a significant other.
But I agree the situation is atypical and probably why comments occurred.