He got an erection from milking them

Tim felt the milk squirting out of his nipples. It was a feeling he never had before, but it was arousing. Immediately his soft penis reacted to it and got hard. "Oh my god, I have tits." He said and saw past the breasts, which he couldn't stop squeezing, his dick getting hard. Tim knew that it was wrong. It was wrong to that he had breasts. It was wrong that he squeezed his breasts. It was wrong to get aroused by it. But it was so good. It felt so good to squeeze milk out of his soft breasts that he couldn't help but let out some moans.

"Seems like you not only love lactating breasts on women, but also on yourself." Dr. Valentine said with a wicked smile, as she now had an idea, what she would try to turn Tim into.