I'm a Commercial Pilot, quite young, n im in a very problematic situation, regarding my beloved.?

You have everything but proof that she is cheating on you. She is lying and she goes out with other guys that have proposed to her? Dump her man and get on with your life. If you dont do it now you will have even a harder time later when she does worse and you really cant take it anymore. Heck who knows maybe losing you will straighten her out and she will come begging. Its possible.