My Boyfriend Has Genital Warts. When We First Got Together

my boyfriend has genital warts. When we first got together they were starting to shrink and seemed to go completely away! Now, in the past 2 months they have came back different looking and a lot of them in clusters. very noticeable. Does that mean he has contracted them again from sleeping around or is it the same virus just coming back? We both went to the doctor for them 5 yrs ago. Is it a different strain possibly?