You don't.
If you did that, she would be uncomfortable. She might not want to talk to you if you just call her beautiful without even getting to know her a bit more. What you should do is get to know her first or even be girlfriend and boyfriend with her.
"je t'aime ma belle petite amie" (a noun like "mon coeur" would be more romantic)
If your handsome or beautiful it makes your cloths look good, which makes you look more handsome and beautiful
just be yourselves and wear your nicest clothes. everyone is beautiful
Absolutely, although there is more to life than looks or beauty. I would be more likely to diet/exercise to achieve my ideal look, but would be more likely to focus on the non aesthetic dimensions of myself to improve.
If he "loved" you more he would break up with his girlfriend to be with you.
Because that is more beautiful.
lovelier, loveliest
Then, unfortunately, it would seem that you really do not have a girlfriend. If I were you, I'd look for another relationship with someone who is more available and also wants a relationship with you. You deserve more and you will find more, just keep looking for the right person until you find them.
because she just wants to see if you would agree that shes more beautiful
You love her because she is beautiful and kind but you hate her because she ignoring you i cant really answer i need more detail!
You would think a girlfriend would be more important than a car. There may be some guys that would like a car better than a car though.