I'm confused, please help?

im dating this guy for the past 2 years and i have a feeling that he's no more into me
i've known him that he flirts about with other chics but that ain't my concern now
he always talks to me only when he's in the need of sex or he wants to do this

i made a trick on him to test him
i made a fake girl's account on kik and started chatting with him..
he kept asking for my phone number and all, but i refused to give him. he also asked for "nude pics" which i denied to sent him
he wanted to meet me but he also kept flirting with this kik girl
last night he called me and asked he wanted to see me, i refused to him that i can't, so he had text this kik girl asking if she was free and he wanted to meet (the same day when he asked for kik girl's nude pics).
im pretty confused, is he trying to play it hard on me? why does he do this? does he want only sex?
why do guys flirt around with many girls? why don't guys stick with a single girl?

I'm confused, please help?
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