How can i tell if he is checking me out?

so i just met one of my brothers friend for the second time. He is beautiful. looks like a buffer and cuter Justin Bieber. and he is really nice. But the first time i met him, i was really overweight, and just over done for how not pretty i used to be. But tonight i saw him and i noticed a double take. and im wearing all sweats today, with my hair pulled in a high pony tail and just mascara on. and i've lost 30 pounds since i last saw him. But i was hanging out with him and my bro and i kept noticing like he would look into my eyes, and look away or he would smile (with dimples!!) and turn away. SO do you think he was just checking me out, or like genuinely becoming interested? Thanks :)