well i don't think it was ur fault... it's natural to be jealous when you really love him.
me i don't easily get jealous but when it comes with "ex", i do get jealous. i guess because they had an intimate past and if they started talking bout this things.. your bf will have some comparison and might lead to deeper meaning with them. if it's just a natural hi and hello that's not a problem. but with the extent of talking bout their past and bout how they were when they're still together, seems like they're missing it.
ur bf should respect how u feel and same thing with his ex, she should respect ur relationship. i'm sure she knew that u r jealous and she should have stop flirting with ur bf.
but seems ur bf value more of his relationship to his ex than you.. well better let him go...
u will find a better guy.

my husband stopped having communication with his ex without me saying it... it was his own decission.
in a relationship you should have both love and respect. that's what i believe. not 'LOVE' alone.