what can I do to get my ex back

Well me and my ex girlfriend went out for about 9 months going into the 10th month she found out that I was talkin 2 other gurls bout doing things with them but never did cause I knew it was never going to be the same so she found out and as well another reason was that I was way to over protective and very jealous and felt discouraged bout her guy friends so. I would question her bout everything and she eventually gott tired of it but then me and her started talkin again and messin around ni it felt great da only thing was that me and her weren’t 2 gether but then on july 4th we gott into a really dumb arguement that we don’t even know who started it and who ended it I tried talkin 2 her the next day about what happened and try 2 fix the problem but didn’t know what to do anymore cause she told me that she didn’t want me no more that she was tired of it and den I found out that she started talkin wit 1 of my suppose 2 b friend bastard and now I don’t know what 2 do anymore what can I do 2 gett her back ?