I understand that those different forms should be a little bit challenging when learning korean. Those sentences, you mentioned in a different way, are almost the same. They just differ when to use according to older or younger people and someone you are not that close to. SARANGHAE is for younger people and your close friends. SARANGHAEYO and SARANGHAMNIDA are formal way to say so that you will say to elderly and someone you are not that close. But actually, you would not say SARANGHAMNIDA to strangers, so in this case, the person should be the one you know well, but must be a bit older than you SARANGHANDA is kind of informal way to express. I think it is used to emphasise your love. I have no idea as to explain SARANGHANMADI. It does really make sense. Was it helpful? hope you enjoy studying korean. have a nice day:D

Yes.. Those are same meaning. When you're saying to younger people and your friends and boy/girl friend too. You can informally say : 사랑해, 사랑한다. You can formally say to older people than you : 사랑합니다. 사랑해요 etc. 좋은 하루 되세요.~!