"suis" is not pronounced as the first part of "sweet" ! it's not soo+wee it's su (the french "u")+ee. souillé = soo+yé (not yay/not yéï), hope it helps :)

I presume you mean "souillé"? In that case, yes, there is a difference in pronounciation. "Suis" is pronounced similar to the first part of the word "sweet," while "souillé" makes the sounds "soo" and "yay," although the final "é" should sound more like the E in "egg" than the A in "yay." Hopefully you don't find this to be more confusing than helpful!