Under what circumstances is it rude to ask to split the check?

When is paying for yourself considered rude?

Tonight I was out with a friend the their family, who were very likely going to treat me to dinner but didn’t say they would. Side note: They are well off, I am not. At the end of dinner I asked the waiter to split the check and he made it kind of awkward, well it was all a little awkward. I have no problem with people paying for my dinner, conceptually it’s great, but I always feel funny. Even tonight when I paid for my dinner it still felt funny.

So I was wondering when is it rude to ask to pay for yourself for dinner or anything really? On a date or at a dinner with family or friends? Your thoughts please, what’s good manners?