Yes, you have to understand those sentences depending on the context. I think "~ㄴ 지" signifies "The action started BUT there's no signification whether the action is finished or not". 밥을 먹은 지 5분 됐어요. = It's for sure that you started "eating" but this sentence doesn't show whether you finished eating or not. So you can translate in English like "It's been 5 minutes that I started eating.(I'm still eating.)" or "It's been 5 minutes that I finished eating." 여자 친구랑 사귄 지 6개월 됐어요. I understand this sentence that you're still seeing her. If you broke up with her, Koreans would say "여자친구와 헤어진 지 6개월 됐어요=I broke up with my ex-girlfrend 6 monthes ago AND I don't have a girlfrend now.". Maybe "~ㄴ 지" is quite confusing but I think you can understand depending on the context. Cheers! :)