How long have you been dating? It involves a lot of primal biology but because we have the biology we do, it makes us behave, and it allows us develop into, who we are. I'll give you the good news first: you're probably about to have a lot of crazy sex. Like the kind of sex where the next day you almost have to break the ice over some casual conversation because you're ashamed of yourselves.
People take a real high brow approach to pair-bonding mechanisms these days but I don't. Your first enjoyable sexual experience creates an impression on your brain probably lasting the rest of your life. It was originally what held tribal marriages together because they did not have personal relationships as we do today. They may have, but women were as servants to their mates then. Even fairly recently this has been true. You've heard the term "lady-in-waiting" or "ladies-in-waiting"? Basically, what we call bridesmaids today (we don't have servants). These were single women that would prepare the bride for a wedding or other occasion. They were not married, "in-waiting" I assume as in 'waiting to get taken as a wife' which is likely why we have "waitresses" and "waiters" today. Single because the married women would have had status and husbands to serve. It was quite the hierarchy.
The downside (if one exists at all) is that the bonding that occurs can be pretty powerful. Once you've reached my age, you may have had so many partners that the bonding mechanism becomes less and less. I have to have a good intellectual and personal relationship because sex just doesn't cut it. Parting ways is just, "Did you get your toothbrush and lotion from the cupboard? Tampons? Okay, baby. I'll call you. Bye!"
But she could get rather clingy, jealous, insecure...etc. So don't fault her too badly for it. It's chemical. But you will have to get to know her now with all the sex and mind games and signaling in the way. You ate dessert, now you have to get to the meat and potatoes of whatever this is, is.
Keep me posted! I'm actually a little envious right now. Will need details.
OTH