Think about it, a wedding band is the ring that signifies your marriage. The engagement ring is a "made up" ring. For thousands of years, even the wedding ring didn't exist. Think about all the poor people in medieval times and back did not have a wedding ring, but you were married.
Then later, some person thought, oh, if I give you a ring before the wedding, that means 'I'm totally serious about getting married'. Then later, someone thought that it would be nice to put a diamond on it. It's a man-made (or DeBeers-made) symbol of marriage. The engagement ring is not in the Bible or Koran or Torah.
Kim Kardashian, Jennifer Lopez and whatever other celebrities got a monster diamond in their engagement ring. Their marriages ended. A diamond isn't forever. But, the money you spent did go to help some South African white dude with the last name of DeBeers to live large.
You need to talk to your woman and ask her what is really important in life, marriage, etc. Because if the ring is important, more important than say affording a home or car or paying bills and not going in debt, then she might not be the one and she can look for someone else who has the cash to keep up with the Jones.