About 2 years ago my ex fingered me and later told me that he wiped his precum with his finger and fingered me, but is not sure whether he did it with the same finger. He said he has only made out with his ex girlfriend so doesn't think he has any STDs. Could someone please tell me if it's possible to catch any STD this way, given that he fingered me with precum on his fingers? If yes, what STDs spread this way?