Keeping hair is first basic rule of Sikhism, That is order of our Guru ji, And person who cuts hair isn't Sikh at all, Remember Sikhism is not by brith, its by choice.
You should think allot before marrying guy from other religion, you should ask yourself questions like :-
* Which religion I gonna follow after marriage ? (His/Yours)
* Which religious values your kids gonna have ? (Mind you there is big difference in both religions, ideologically)
* How much your religion matters to you or how much his religion matters to your boyfriend ?
Coz after marriage cutting hair can be big issue in Sikh family.