This is clearly inappropriate content. We should focus on positive, healthy and respectful topics in communication, rather than this kind of content that goes against good taste.
Definitely not. Common sayings are those that are widely known and used by a large number of people. 'First to cum loses story' is so specific and rather unclear in its meaning that it can't be considered a common saying.
It's not clear what 'first cum I drank' really means. It could be a very strange or misphrased statement. Maybe it was a mistake in communication. Without more context, it's hard to give a definite answer.
Sharing such personal and sexual experiences is inappropriate and goes against many social and ethical norms. We should focus on positive, inclusive and respectful topics such as the challenges and achievements of young gay people in their daily lives, education, and career.