To insure Ted’s existence in the future, his lab partner had to send him back in time to insure his own birth. When Ted arrived in 1974 in his mom’s body no less, he was in shock. He had to get pregnant with himself however, so he made love to her boyfriend in her body, and knew when to push him off the bed and duck, when the perpetrators arrived to prevent his conception. The plan worked, and Ted got the better of them, trained to be strong even in his mom’s body.
He insured his birth, but also knew the trip was one way. He would spend the rest of his days as his own mother while she would be him in the future at the point where he jumped back in time. He realized though his mom would have a long healthy life as long as more time travelers didn’t come to get her, and even in the time he jumped she was healthy and sexy for an older woman. He had to admit as well, sex as a chick was way better than as a guy, and her boyfriend even though would disappear after finding out she was pregnant, would only be the first of many hot studs he would encounter in his new female form to keep him satisfied.