In what way is the game ruined?
Ellie lost a lover, not a friend. She had strong feelings for Riley, and it is hinted that they have been on dates before. If it was the same but with a boy, you would not have been offended. Ask yourself what you find so offensive.
We knew that Riley was extremely important to Ellie, it was hinted many times in the main game. Plus if you read American Dreams, it does feel more than friendship between the two. Ellie expressing her feelings did not come as a surprise to me. The DLC was beautifully written and acted. It did not feel forced and their relationship was moving.