Nov. 24, 2011 -- A father of 4-year-old twins claims his ex-girlfriend stole his sperm and impregnated herself at a fertility clinic, and he is now suing for full custody of his sons.

Joseph Pressil, who currently lives on New York's Long Island, had moved to Houston to be with his ex, and had even bought a house there. Now, he says, he has no plans to go back.

"This was so shocking to me," Pressil told ABCNews.com. "I met her in Miami, Fla., in May 2006. I remember that day," said Pressil, 36. "That was the beginning of the end."

The couple broke up at the end of November that same year and three months later, she told him she was pregnant. Paternity was eventually proved with a DNA test, and Pressil, a telecommunications manager, began paying more than $800 a month in child support.

Then, this February, he found a receipt in his mailbox for sperm cryopreservation.

Confused, he called the company that had sent him the paperwork, Omni-Med Laboratory. It referred him to the Advanced Fertility Center of Texas, where a manager asked him to sign a medical release form.

Pressil told ABC News that he never heard back, so he decided to pay a visit in person. According to the lawsuit, the manager said the clinic assumed he and his ex were married when they performed the successful in vitro fertilization procedure that resulted in the birth of his twins. The clinic refused to share anything more because of HIPPA -- the Health Insurance Portability and Accountability Act -- privacy rules.

Pressil confronted his ex, who according to him said, "Oh you're not stupid. I thought you knew."

Now, he says, her behavior during sex makes more sense.

"At the time she was giving me these condoms, and she said because of her fibroids these condoms were not lubricated, and would not affect the fibroid enlargement," he explained. "Every time she would give me these condoms after the sex she would leave the room. She'd come back, give me something to drink. We always had sex in the morning and she'd say she had to go do something. She would leave about 10 or 15 minutes afterward."

According to the Mayo Clinic website, sperm ejaculated outside the body can survive, at most, for a few hours.

Pressil says he never discussed IVF with his former girlfriend and they had never intended to have children.

Under Texas' Uniform Parentage Act, an unmarried man must consent to the use of sperm for assisted reproduction, and that consent "must be in record signed by the man and the unmarried woman and kept by a licensed physician."

The clinic claims to have that document, but Pressil told ABCNews.com his signature was forged and "doesn't match."

That's why Pressil's lawyer, Jason Gibson, says this is a case of theft.

"If they've got him listed as patient they need his consent to do anything," says Gibson. "They violated their own policies and procedures by not getting that consent."

Danny Sheena, the attorney who represents the clinic, could not be reached by ABCNews.com, but this week he told KPRC-TV in Houston, "[Pressil's] insurance was billed for it, and we do know that his credit card was used to pay for the visits. … His presence in this thing, as far as my client is concerned, is absolute."

Pressil said his ex-girlfriend was an exotic dancer and didn't have insurance of her own. Because they were domestic partners, he added her to his insurance after she told him about her fibroids, he said.

The ex-girlfriend's lawyer, Derek Deyon, told ABCNews.com that Pressil filed the lawsuit to avoid paying child support, and that his client denied ever taking semen from a used condom.

"They [the clinic] had to test his blood and her blood for STDs," Deyon said. "The clinic is saying they had his blood."

But Pressil said he never gave a blood sample.

He currently has joint custody of the children, and plans to seek full custody "because of all her scandalous ways."

In the lawsuit he's asking for a jury to determine how he ought to be compensated for child support and mental anguish.

The entire incident is simply "embarrassing" he said. "How do you let someone do that without knowing?"