It is not necessarily good nor bad.
It just depends on the circumstance.
A guy may say that a girl is too sweet because she always makes him feel better whenever he is unhappy or worried about something.
Whether he is having a really bad day or having some kind of hardship in his life, she tends to be able to better his mood or alleviate his concerns.
He has become aware of how she is able to say exactly what he needs to hear in these moments.
Hence, he comes to rely on that.
He may say that the girl is too sweet because she is so consistent in lifting up his spirits.
If this ultimately leads to the guy beginning to confide in the girl about romance or love issues as far some other girl he may like, he really only sees the girl as a friend.
Once it gets this far, he is showing that he has no romantic interest in this sweet girl.
However, this is not always because the girl is too sweet.
He may have never actually liked the girl romantically to begin with.
In essence, he may have always looked at the girl as someone that could possibly become a friend and nothing more.
If this is a guy that you like romantically who tells you that you are too sweet, he may have just always looked at you as a friend and nothing more.
Thereby, the fact that you tend to be really sweet to him wasn’t the reason why romance never developed between the both of you.
He may have never been feeling you in a romantic sense from the very start of your relationship or interaction with him.
In another scenario, a guy may say that you are too sweet because he is trying to gauge whether this is truly who you are.
In other words, you may simply be too good to be true.
Perhaps his experience with girls has not always been so positive.
Perhaps he has had some girls act all sweet to him in the past, only to end up being not so sweet in the end.
In essence, he may be cautious or somewhat doubtful of girls who come off as too sweet in the beginning.
He may have fallen for some of them in the past and has now chosen not to be so fast to fall for one until he is absolutely certain that the girl truly is this sweet by nature.
Hence, you could be dealing with a guy who says that you are too sweet because he wants to see whether you will take the bait and ultimately show him a darker side to you.
Indeed, he may be intrigued by you.
However, he doesn’t want to be too hasty in how he goes about interacting with you when it comes to romance.
By saying that you are too sweet, he may be trying to see whether you become so self-conscious about this that you choose to either start avoiding him or you suddenly start acting differently.
Again, he may be trying to gauge just how genuine of a person that you have presented yourself to be.
In a scenario like this, if you are interested in this guy romantically, you should be consistent in your behavior.
This way, in time, he will come to trust that you are genuinely a sweet person and this could lead him to consider pursuing you romantically.