Well the most common way to say it is: 사랑해요 (Saranghaeyo) but intimately this can be simply said — 사랑해 (Saranghae). You may also hear it uttered this way 너를 사랑해 (Neoreul Saranghae) or 너를 사랑해요 (Neoreul Saranghaeyo). Note that 너를 (neoreul) is added which is actually 너 (neo which means you) and the object particle 를 (reul) so the word you becomes the object of the verb Saranghae. This is often dropped specially if you are talking directly to the person which makes ‘you’ obvious during conversation. You may probably heard of 사랑합니다 (Saranghamnida) which is the formal version, well this is not commonly used during conversation. As mentioned in previous post verb ending -ㅂ니다 is formal polite, the style that you use for formal conversation. This however is widely used in some songs.