I think it would be easier to find a new boyfriend who appreciates you *as is* than it would be to try to change yourself into a trivial little bimbo, and anyway, I doubt that is what he really wants. Have a little more confidence in yourself, because I doubt it is your level of seriousness that puts him off - but your obsessing over whether or not you will lose him might become tiresome. Insecurity is very unattractive. Fake it (confidence) if you have to, and it will feel more natural after a while.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?