Should I be concerned at all?

[penguinash2010]

My boyfriend of 2 years has an ex that he says is "crazy". They literally broke up once a month when they were in High School. Now he is 25 years old and just graduated with his Master's Degree. We have plans of engagement and I have a promise ring. We are just waiting for me to start my student teaching and internship so we can be engaged that entire year so we can get married when I graduate. This morning after picking me up from class he told me that he checked his Twitter account and saw that his ex Lacy was following him and sent him a direct message saying "hey". He immediately blocked her. Well I looked her up and although he blocked her, she still tried to send him a message asking him why he blocked her. What does she want with him? They haven't talked for almost 5 years and 2 of those years has been with me. She used to stalk him on AIM and stuff but he told me all that. He could have blocked her and hid it from me like it never happened, but instead he was upfront with me and honest about it. But what should I think here? What if he gets curious to just talk to her. What if she is screwing with him again and wants him back? I can't take that. She is 23 and acts like a 14 year old psychopath. I don't need that kind of drama. I am about to graduate college in a year or so.