you'll know if the guy really likes you if he will tell you he likes you. never assume.
but of course that's not enough... he will also show it through actions... he will definitely show you what he feels for u... (by calling u, courting u, giving u gifts, asking u out, treating u to dinner/lunch,etc)
but the most important thing u should look for is CONSISTENCY.. hindi palitaw.. u know what i mean? minsan may text, minsan wala, minsan parang may gusto, minsan wala,... moody? nah..
and if the guy is really putting EFFORT to pursue you and win you over.
and then you wait for, let's say, months and he's still like that,
then u can say may gusto nga sya sayo