he is not prepared to take things any further.
He doesn't get the reaction he expects when he tries to impress you.
or maybe he is an A...i have heard guys say over and over again..."she's too serious" about me and about other girls...."too complicated" is the new "too serious"...forget about it unless you hear it again from someone else....do you have any friend or family that you know will be honest? Ask them...since they know you
My guess is that he means one of two things. Either he can't figure out what you want from him because you give off mixed signals so he's unsure whether you're really into him or not... or he means that you have a lot of emotional baggage that causes all sorts of drama. (For example -- crying spells, needing a lot of reassurance that he cares about you, being overly jealous and possessive, etc. are all things that would be a huge turnoff to most guys.)
Probably that he thinks you're too complicated.
Maybe he thinks you fuss about one aspect of your life disproportionately to others. Maybe he just doesn't want a long-term relationship right now but doesn't want to admit he has commitment issues.
Because he's holding off for something better. If he can't find something in the immediate future, he wants to have you around just in case. Of course he won't say that outright to your face.
I don't know you from Eve, but you're not unattractive. Why is he considering new girls if he's already in a relationship? That's like using company time and resources to look for a new job. It's a good way to get fired and a sign of a scumbag.