Feeling lost and don’t know what to do!!

32M, Shifted to another country on student visa and changed fields to be with my long time gf (10+ years) after coming here i came to know that she was seeing someone else for past 1 year and is planning to get married to him in next few months. Our relationship was not very great being in long distance and i had hoped that things would improve once i come close. Now she is living with that new person in the same city and doesn’t even meet me. My course is in another field that i am not very good at and was advised by her to select this. I was not aware of all this and was informed by her 1 month after i reached, Completely broken as a person and took 3 months to just contemplate as to why she did this to me, I confronted her and she told me that she was not sure that she was going to Marry him and whether his parents would agree.. I just don’t know how to approach life now. Everything i build for last 10 years both personally and professionally is gone and i am totally lost. Would encourage some advice..