My gf left me 4 a dude plz help?

im 18 and 100% i been dating the same girl off and on for almost 2yrs (it will be 2yrs later in august). i have only known her to date girls (she told me she was gay but had flings with guys). sunday she said her and this dude (who she only knew 1week) met up and did stuff together. she broke up with me and said we can try to be friends but if you mention anything about a relationship you are gone. i said that i will work on myself and will try to win her back. she says that she wants a bf and not a gf. she says she doesnt know if she is gay now. it pisses me off and it hurts. she says its because im jealous. im saying its because you told me something for 2yrs and i find out it could be a lie. she only knew him for 1 week!!! i think all he wants is . but how do i get over the pain and heartache. this is the worst i ever felt.he broke up with me and said we can try to be friends but if you mention anything about a relationship you are gone. i said that i will work on myself and will try to win her back. she says that she wants a bf and not a gf. she says she doesnt know if she is gay now. it pisses me off and it hurts. she says its because im jealous. im saying its because you told me something for 2yrs and i find out it could be a lie. she only knew him for 1 week!!! i think all he wants is . but how do i get over the pain and heartache. this is the worst i ever felt.