Why did he say that to her?

so my bf was talking to this girl on fb. which apparently is the same girl who told him she loved him a couple months ago. i never worried about it bc i had no reason to be. but today i guess that had made a plan to c her but it didn't work out. and she told him yo te quiero mucho. (i love u a lot) which he replied good:) aww thanks. she just put yeah and then he put yo tambien te quiero.( i love u too) wtf!! i will talk to him about it tmrw when i c him but why is he telling other girls he loves them and most of all her? i talked to him a little while ago and he acts like nothing, nothings wrong hes not doing or saying anything. i havent brought it up directly though. but i just wanna know why? ugh help please anyone. some advice is greatly appreciated