If you have access to a faculty advisor, something you might do is schedule these two actors a meeting with that advisor to discuss the importance of professionalism. As the SM (and a fellow student), your words only carry so much weight. A faculty advisor saying "No, sorry, this won't cut it in the real world: you need to be on time, you need to be in touch, you need to keep the affection to appropriate times and places... and if you can't figure that out, you're in serious trouble" would drill the point home much more effectively, and would allow you to ramp up your own rhetoric (and, should it come to that, consequences) if the situation doesn't improve.
This with the caveat that it depends upon the advisor's schedule, personality, relationship with you and the show, and so on.