What do i do?? i always get bored of my relations even the ones dat seemed to b da one?

i have been dating alot. but i ve been bored of all da casual datin nd stuff.. so since da last year nd a half i ve bn consciously tryin to avoid meaningless relations.. nd when i do date start datin somebody its always been somebody really nice nd with me thinking of a more serious relation... but even when everything starts off wonderfully initially it all goes away within 4-5 months. all the spark all the interest juz vanishes for me.. it seems all my relations come with an expiry date.. what should i do?? help