Advice on his ex and him

My boyfriends first relationship was when he was 16, it lasted 7 years until he broke up with her (age 23)... And then some.  He hooked up with the same girl a few years after that and then when he was 27/28 he got back in contact with her.  They hooked up again and she broke up with her current bf to be with him.  After my bf met me he completely cut her off again.  She's a lawyer and sucessful so sometimes I get a bit insecure.  But for some reason I can't get over the fact that they were together for so long.  I feel like he may still have feelings, though he denies it.  Should I email her?  I want to know how it really ended..