Since you’re long distance, and you know he’s flirting with other women, rather than make him stop (you’re not his mother, and I’m quite sure you don’t want to be), consider why he’s doing this. Either he’s lonely and feels that the flirting is harmless, or he’s looking for someone else because he’s not committed to you. Your fear that he’s going to see another woman when he’s in Germany visiting you, doesn’t give a reader much confidence in his commitment to his relationship with you. Is there a good reason the two of you aren’t in the same city at this point?
It isn’t clear why you were having problems. You mention that you “take his air away” and that he says you’re “destroying his feelings” but I’m not sure what that means in real life. If these problems you’re insinuating are fixable, then you can try working on them, but if they’re not, I hope you’ll do what I said and pick an end date on the relationship at which point you realize this man is giving you what you want for yourself, and that the relationship is where you want it to be, or if not, that it’s time to move on.