Book about a man who found out he was an alien robot and eventually started running from both his makers and humans

There's not a lot here to go on, but my gut tells me that you're looking for The I Inside by Alan Dean Foster.

The aliens are the "Syrax" and they created the hero, Eric Abbott, to learn the secrets of the human GATE technology (instant transportation over interstellar distances). The thing is that Eric doesn't know he's an alien construct, and doesn't actually wish to betray humanity.

The plot kicks off when Eric sees Lisa Tambor (Lure Tambor Four) driving by in a vehicle and falls uncontrollably in love with her. He chases after her, and despite the efforts of her controllers (lead by Kemal Tarragon) to get rid of him, Eric finally meets her.

Lisa is an "artison," an artificial person, designed to be attractive to people who will be psychologically suitable for Earth's two colonies. Eric doesn't fit the profile, but keeps seeking her out anyway. Even though her programming is intended to keep her from falling in love with any of the men she attracts, she finds herself falling for Eric anyway.

Eric resists increasingly vigorous attempts to dissuade him with increasingly inhuman displays of speed and strength, and finally plans to escape to a colony world with Lisa. They disguise themselves as technicians to get into the GATE terminal where the Syrax reveal they are still tracking Eric; they enable a control device they've implanted in his brain, but he resists the device long enough to destroy it and Eric and Lisa escape.

Eric is told he's not human:

"You had an altercation in Nueva York, in Ms. Tambor's home. In addition to a lot of other blood, you left behind a very little of your own. Like everything else at the scene it was studied intensively in hopes of learning something about you. It's very good blood, but it's not natural."

[...]

"In a suburb of Greater London you broke out of a prison hospital by running through a solid concrete wall while filled with enough dope to lay out a dozen weight lifters. And lastly there is the still unexplained business of your departure from an enclosed office in a building on the shore of the Thames, in London. Six reliable witnesses were within two meters of you when you both vanished, even as you were about to be shot. Where did you go, Eric, and how did you do it?"

Construction. Creature of the Syrax. Good blood, but not quite natural, oh, most definitely unnatural.

Eric just wants to be free of both Earth and the Syrax:

Jeeter stared into his friend's eyes. "Tell me something, Eric. If the Syrax arrived here and approached you, would you turn over the information they want?"

"No. I owe them nothing, just as I owe mankind nothing. Neither has any claim on me. All I want is the chance to live out my life with Lisa as quietly and inconspicuously as possible. I've made real friends here—you, Madras, others. In my opinion, you owe the governments of Earth no more than I do. We've all been lied to and we've all been used."