Is it normal to be this attached to someone

I think I may have a bit of a problem,
something that i always secretly knew... because it's happened time and time again. When I become emotionally and physically connected with someone I lose all grasp of reality. I throw myself into love whole heartedly. I'm eager to give myself over to another. Becoming more and more like a submissive. Of course i understand that most people do this to some extent but for me it's a bit different. Almost to the point where i don't notice how bad it gets. Attachment is huge problem and I'm confused to where this is stemming from. I'm not oblivious and I have seen both the negative and positive effects of being this way. My happiness is solely based on my significant other. Everything i do, i want him to be with me. Don't get me wrong, i like to be alone too, especially to catch up with all my "girly" TV shows, to do my nails, have a nice relaxing bath, read a book etc but at the end of the night i still want him there laying beside me. We don't even need to touch, just having them beside me brings me comfort. I find that I am at my happiest when that special someone is with me, experiencing life by my side. Which sounds cute, but can also be too much for the other person to handle. And i understand that. I also dislike that fact that my mood is always changing to suit their mood. If he's sad, I'm sad... and when he's mad, I'm mad. And the worst possible scenario is when he's distant, I feel depressed, lost, and don't know how to act, i don't know what to do. When i don't know whats wrong it clogs my mind and i can't think of anything else. I take seldom talking it out with others, and researching my scenario online. Why am i like this? is it normal to be this attached?