每日吃瓜

please help! I got given a rather large Ficus Retusa Microcarpa and it had been doing really well for about a month. Now all of a sudden a lot of it's leaves are turning yellow and falling off. I had a smaller one do the same thing a few months ago (It re sprouted but now I think it's officially dead). I really want it to survive because I can imagine how much it would have cost. I water it rather regularly and I spray it almost every day. I haven't pruned it (I don't know how) and I have it by a windowsill. these photos aren't great and it is getting worse:(

It looks like the leaves that are yellowing and falling off are deep in the foliage, which means, they are the ones not getting any light...so that would be nothing to worry about.. have a look at ficus care.