Yes , my gut tells me theres another dude. Also I hate to say it but she is probably banging him, that’s how she made up her mind to be ruthless to you.You know alot of the time it can also be the case that she just found someone closer to her and dropped you for him. Especially if she changed more or less over night, the point is that it doesn't have to be about something you did wrong. Then again, they can fall out of love over night too so she could've just "decided" but more often than not they start to get over you while being together with you, the problem is that we just don't see it because we're so full of lovey dovey emotions that we're blind to all the signals... until we get more experience or start reading about it in places like this. These things always tend to fizzle out unfortunately. You really need two dedicated people from the start to make it work and optimally there needs to be some relocation happening within the first 6 months or as soon as possible.