>>352838071
They fell in love way too quickly, it'll pass. They also confessed way too quickly too, very bad signs. Basically these things are sign that the person has very little introspective ability and acts according to their emotions and how they feel rather than any kind of guiding principles. 
Big warning signs. 

If you like them back then keep spending time with them I guess, but they're gonna be meltie/drama prone. Recommendations for this are slow letdowns; try and drift away slower over time, getting them unaddicted to you as best you can. Leaving too quick will trigger a big response so generally be careful to not go in any deeper and very gradually back out.. like over months. 
Also make your own feelings clear if possible.