So when I started my relationship with my boyfriend he said cute things and we talked cute to each other but after some time (we haven't been dating a lot) he just stopped and he avoid saying those things and maybe even "I love you" but he always says it is that he doesn't feel it, that he just don't say it (not as often). He also said one day that even tho he is not that sweet, it didn't mean he doesn't love me. I started thinking maybe I did something wrong but then I think I am overreacting and overthinking things. Because if he didn't like me or wanted to be with me, I think he would've left already (meaning be out of the bf relationship). But, we cannot always be corny or say cute things, right? That could be a reason too, right?
No one is a mind reader. Try telling him how you feel about saying cute things and that you miss them. Also, ask if there is anything that is affecting his feelings; maybe something else (family, work/school, etc.) is taking up most of his attention. Finally, think about yourself and how important is it to hear those cute things. Sometimes we put too much emphasis on external praise to fuel our internal happiness.
When relationships start out they usually go through a honeymoon phase which looks and sounds a lot like what you've described. There is a lot of initial excitement and strong feelings because of something new. Things don't always stay the way they are at the start of the relationship but that isn't necessarily a bad thing. These initial experiences can be replaced by a more stable and low level sense of caring and dedication later on if two people are right for each other.