No, it is not. Since you are speaking of a future (and therefore uncertain) event, present causality does not exist. Grammatically and stylistically, you should say: "My English would probably get better if I were to marry a native English speaker". Even that construction, however, does not cover all the possibilities. Technically, a native English speaker is someone who is a natural-born citizen of England...and one would therefore want to marry "someone who speaks English as his/her native language". Confusing, yes? Don't give up!