A pick-up-artist in my class is trying to seduce my girlfriend

He is good-looking and to put it briefly; he knows how to play this love-game. I know he is a PUA, because I overheard him talking about "the game" and "wingmans on parties" a few days ago.
I moved in with my gf a few months ago and we have been together for 1,5 year. The "spark" and "honey-moon-period" isn´t as it was in the start, obviously, and we are only 20 years old both of us... you get the point. Our sex-life has decreased after school start too (studying economy, takes alot of time), so we can have sex 1-2 times a week without it being a problem. I get her off, she gets me off. Simple as. I think we see eachother too much as well... we live together, is in the same class and have a small social-circle due to moving to another city. In other words, I think we spend too many hours together (not healthy).
Apart from this, there is this PUA I mentioned. He has basically turned out to be a "freash breath" in her life it seems. He is new and she doesn´t know him to well (compared to me, the guy she has been with for 1,5 years). He really knows how to speak and flirt with people, and I have understood that it is my girlfriend he´s after. (Sometimes I would love to have an ugly girlfriend so no boys would try her, but that would be boring... so nevermind. Better with a beatiful one). Anyways, she has started to talk alot to him during classes and she has that "im in love" expression on her face when talking to him. I know her.
SO WHAT AM I SUPPOSED TO DO?
I guess all guys with girlfriends experience this from time to time. The famous orbiter. I have made a plan and I want you to share your opinion on it, and maybe add your recommendation too ...
- I WILL NOT SHOW SIGNS OF JEALOUSY. I have managed to "not care" so far and intend to keep doing this. I will let her speak as much as she wants with him and not tell her to stay away from the bloke. Why? Because I would rather catch her than make her hide things behind my back (like talking to him on facebook when I am in another room etc).
- I WILL FLIRT WITH OTHER GIRLS? Is this a good or bad idea? My game is there so if I want to, this would be a simple task. Opinions please.
- I WILL GIVE HER MORE ALONE-TIME! Not being with her 24/7 might be a good idea, so I am going to do something about this.
This will be my "case study." Ill try to update once in a while. Please add comments.
- Consistence