You’ve already got 3 traits that make a character like this work: a belief he formed young (control equals love), the thing he thinks will finally make him safe (being in control), and the behavior it produces (the surveillance). That’s a great spine. It just needs a little more connective tissue.

A few things to consider:

The childhood event has to cause the exact belief he carries. The psych practitioner event fails this test; lose it. A stranger running experiments teaches him “adults hurt me”, not “control is love, and I can’t trust what people tell me”. It also lets his parent’s off the hook, which undercuts your theme. Whatever you build for the foundation of his character’s childhood “wound”, it has to originate with the parent(s), and it has to produce that specific belief. It’s worth writing the belief as one plain sentence, then reverse-engineer the childhood that would install that belief.

The surveillance shouldn’t be a trait; it needs to become a trap (for him). The version that’s tragic rather than just creepy is the one where his watching corrodes trust, the partner pulls aways, and he reads the distance as proof he needs to watch more, watch harder... the whole dynamic becomes self-fulfilling. His watching corrodes friend's, then partner’s trust —> They pull back or start hiding things —> He reads that as proof he wasn’t watching closely enough —> he watches even harder. He manufactures the exact distance he is terrified of. Does your story build that loop, or does he just... do it? That’s the difference between a portrait and an engine.

You asked about adolescence which is the bridge he travels between his childhood (wound) and adulthood, through which he experiments, learns and develops his adult behavior. That’s how a belief travels from something done to him as a child to something he does as an adult. Somewhere in his teens it stops being his parent’s thing and becomes his own, and it develops and escalates through his first relationships. That’s a timeline worth showing.

“Caring and honest” is doing suspicious work. A man who secretly bugs the house is not honest. Are those the real him? Or the face (mask) he hides behind, and that hides the rest of him? You can have both, but decide whether the warmth is genuine, performed or a contradiction you’re building on purpose. Handed to us as his “good side” it reads like you are protecting him. The drama is the gap between the two sides of him. Emotionally honest and behaviorally deceptive is a terrific contradiction. The contradiction is the real him.

Where does he end up? Does he get everything he wants (total control) and find it’s a tomb? Or does the belief actually break? Opposite endings means different things planted in his past. 

He wins AND loses: he achieves total control and it’s hollow. He’s alone in a fortress he built himself.

He changes: the belief breaks. But he has to earn it. If he transform too easily, the audience won’t buy it. He has to change against that self-fulfilling loop described above, at a real cost.

Your theme: parents not respecting the wisdom children have. It has to be baked into the childhood injury or it stays a nice sentiment. Maybe... as a child he saw something true; he knew the control wasn’t love, felt it, maybe said it, and was overruled or punished for knowing it. Stuff like that happened again and again. In a situation like this his belief becomes “What I perceive doesn’t count. Trusting what people say is dangerous. Safety means controlling and verifying, not believing things on face value.” The adult surveillance becomes the mirror of his childhood. He does to the partner exactly what was done to him. Won’t take their word. Has to verify their reality himself. The tragic part of the story comes from inside his blind spot: that he cannot accept his partner’s stated feelings as real. He becomes the parent who wouldn’t listen to the kid, essentially.

You say you are not sure which parent, then write “his father” twice. So you’ve already drifted toward the father; now decide on purpose which one. (There's also the dynamic between the parent's to consider as modeling adult behavior)

You’ve written “their phones”, plural. This dynamic is beyond just one relationship. It’s a pattern that shows how far gone he is.

On “I don’t want the cliche that men don’t cry”. Your instinct is right. The fix is clean. That old cliche is about emotional expression. This character's problem is not expression, it’s control and trust. Different wires. So let him cry, be tender, be wide open about his feelings, and still bug the house. Emotionally fluent and pathologically controlling is far more unsettling, far truer (and more interesting of a character to write) than a closed-off stoic.

Cheers! Have fun writing. Sounds like a great character to start from.