Brock's a virgin. He has never known the touch of a woman. He spent the first chunk of his life running his absentee father's gym and looking after the kids. Brock would make an excellent mother. Maybe a decent husband. But a lover? Hell no. Now look at Professor Ivy. Those long legs. Those big, bouncing breasts. She's no slut, but you know she's got some experience. She's older than Brock, an expert on anatomy and knows a trick or two. What Brock was chasing was acceptance, love. He never tries to kiss the girls he flirts with, merely an exchange of words. He makes romantic gestures. He cooks, he cleans, but that's about as far as it goes. And one more thing. Ivy has been alone with only three unattractive, immature female assistants for a long time.
So the first time they're alone together, it's a bit like a Pokemon battle. Except Ivy already has Sword Dance, Rock Polish, Shell Smash, Belly Drum and Calm Mind going. Brock's in Little Cup and only knows a few Learnpool moves, all STAB. Ivy physically demolishes him. The first session doesn't last 3 minutes. She's barely warmed up and Brock has already spent himself. You can't blame him. First time, a woman as hot as that, plus that thing she does with her tongue.
Weeks pass and every session is the same. She can't make him last long enough. She teaches him how to tease before pleasing, foreplay goes on for hours so they can climax together once. Just once. She's not satisfied. Brock is a marvellous househusband but in the bedroom, he's not the Onix he was expected to be. More like a diglett. Eventually, she gives up. Brock feels dejected. He waits on her hand and foot, hangs on her every word, gives everything he can for her, but it's never good enough. The breeder lack what it takes to breed. Lost for what to do, the mere mention of her name brings him to a depressive, heartbreaking halt, reminding him of the woman who was just too high a tier for him to please.