The New York heir to a $100 million ice cream fortune has acted like an abominable monster toward his estranged wife — paying a team of investigators $140,000 a week to trail her every move, hacking into her smart home system to screw with the lights, music and temperature, and even demanding that she have sex with him in order to see their son, according to a new lawsuit.

“I surrendered for my son,” Susanne Gold, 45, admitted to The Post in an interview.

“Instead of holding a gun over my head raping me, he would hold my son over my head,” she said.

Gold, 45, wed David M. Smith, 52 — whose father, Richard E. Smith, was CEO of CoolBrands International, the company behind Chipwich and Eskimo Pie — in 2008. At the time, she’d recently given birth to their son, who is now 11.

But the Plainview, New York, resident said there was no honeymoon period with Smith, who allegedly threatened her with a “bombardment of legal proceedings” if she didn’t become his wife.

“Smith dragged her to a Justice of the Peace, and they were married,” she says in her Nassau County Supreme Court suit. The couple never lived together. Instead, he bought her a home in Plainview while he stayed in nearby Roslyn.

Since the marriage, the multimillionaire heir “has engaged in trench warfare against” his spouse, the suit says.

“With nothing to do with his time, except collect dividends and clip stock coupons, [Smith] spends his abundance of idle time undertaking actions to harass her with a variety of malicious, vengeful actions,” the suit says.

He hired the International Investigative Group at a rate of $140,000 a week to “track, surveil, and follow the plaintiff and her family and friends, around the clock from 5:00 a.m. to 12:00 a.m., seven days a week, inside and outside the privacy of her home,” the suit says.

The PIs even shadowed Gold to a Long Island domestic violence shelter and on a recent cruise vacation, according to court papers.

The firm’s attorney, Lowell Sidney, said his clients have “always conducted themselves professionally.”

“They’ve uncovered or gathered significant information on this case and now the plaintiff is attempting to taint their discoveries through vexatious litigation,” Lowell explained.

Smith took it upon himself to torment Gold “by using computer applications to gain control of the plaintiff’s vehicle and lights, music, and temperature in her home without her consent,” according to court papers.

He also made sex with his estranged spouse a “condition for granting her time to spend with their son,” the suit says.

“If I didn’t sleep with him, unfortunately, I wouldn’t see my son for months at a time,” Gold said.

Smith filed for divorce from his wife in January. The case is still pending. She hasn’t seen her son since October, when, she says, she refused to sleep with Smith at the behest of her family.

“Since the defendant David M. Smith does not mind paying for services, he should hire a prostitute to satisfy his needs instead of continuing to prey on this plaintiff,” the suit says.

Smith and his attorneys did not immediately return calls requesting comment.