It doesn't feel fair to be upset at the fact that Seo is an active porn actor. It's fine to be unhappy at the idea of you, personally, dating someone who works in the adult industry, and it's fine to compare your reaction to Natori's. But a recurring theme in this manga is Seo being an actor and how they maintain their relationship around this fact. They've mentioned multiple times that it isn't easy, and that having a stable relationship with someone outside of the industry is rare. But that's the point. It's NOT easy. It's NOT all sunshine and rainbows. They're working around this fact. (con't)
Besides, it feels a little close-minded to reserve this disdain for porn actors, imho. Regular actors do kissing and sex scenes all the time, and many of them are in relationships and/or married. The entertainment industry is complex and it can be hard to maintain a stable personal life outside of it. Again, that's the point of this manga.
If you don't like it, there are countless other BLs where a porn actor leaves the industry after finding a lover. Read Walk on Water, Life Ain't so Bad, Melt at Night, or anything else. But I don't see the point in complaining about it here when it's a main theme of the story.