Should I break up with her or confront her?

[verb]

So I don't have a twitter, but i found out my girlfriend following her ex on twitter. however she is not friend with him on FB and i have one. She also cheated on me with him, but its been over a year and she's been completely committed to me. But she created the twitter this November which means she followed him recently. Should I be upset or break up with her over this? She is a lovely girl and buys me everything and tells me she wants to be with me forever.
To the guy who responded- I love her because I fell in love with her personality. I just said she buys me things and tells me she loves me cause she acts like she is realllllly in love with me. But why would yoiu follow your ex on twitter, or in that case do anything to get involved with him when she cheated on me?