Is this a sign that my Boyfriend is cheating?

I have been with my boyfriend for 1.5 years and I asked him to marry me several months ago and he said yes.After I asked him to marry me,I've been noticing he's been more attentive to me.He takes me out to restaurants more and actually pays the bill without asking me to chip in,buys me gifts and flowers which is totally out of his character.I keep having this feeling that he is cheating,Am I paranoid or is this a definite sign?