Why do this Christain have poblem with other religion? Why cant they think we all are one?

I'm 22yrs old.n i'm in a committed relationship with a Christain girl for 3yrs. We've spend lots of good time.n most of time,c share n read bible 4 me.m But whenever she brought topic bout religion.i simply cant help myself and her. I dont know how to convince her. At the beginning of our relation, i thot,as yr passes c'l b mature n difinitly understand.. Bt aftr this long yr.of relationship she wants me to change my religion.. As a man,i got responsibilities. And now she define love is nothing b4 her jesus...i'd seek help 4m many expert,paster and even my parent.most of them tel me never give up.c'l understand n realise dat I'm more important than any1 else. I'd given a very fair chance to her suggesting that,aftr we got married,i'l join ur religion n she must also do the same..c decline. According to me, God make love for Human,bt Human make religion to hate people.. I even thot of changing but dat wud b a very stupid of me. I love her more than any1 else. C is also very heart broken.she kip crying whenevr we talk. I startd ignoring her.bt she's nagging me around. I really dont knw wat sud i do.i also dnt wana lose her.. I pray each nyt to God to make her mature fast n come to think that God make love 4 people bt nt to love God 4 whole. But having a love relation after telling me that Love is nothing n i'm less important.this is very bad 4 me. Tell me how should i convince her.?i really dont wana lose her. And after all i'm very sincere to her.. I can handle those problem by cheating but that wud be a problem in future. So pliz help me. N now the problem is that i become so communal,i began to hate christain.