18M attracted to my dad’s girlfriend (35F) and it’s getting unbearable. Need honest advice.

I (18M) live with my dad (42M). He’s been dating “Sarah” (35F) for about a year. She’s not my stepmom legally, but she stays over a lot, cooks for us, helps around the house, and acts very maternal toward me. That’s the problem.

I’ve always known she’s attractive, but the last few months, I’ve started feeling genuine attraction, not just physical. She’s funny, kind, easy to talk to, and pays attention to me in a way my own mom never did. My dad works late most nights, so it’s often just me and Sarah watching TV or eating dinner. She’ll ask about my day, remember small things I mention, and sometimes put her hand on my shoulder or knee when she laughs.

That’s where it gets awkward.

A few weeks ago, she hugged me goodnight (normal) but held on a few seconds longer than usual and said, “You’re turning into such a handsome young man.” I couldn’t sleep that night. Last week, I was helping her reach something on a low shelf, and when I was behind her, I could see she was wearing a leopard print thong through her jeans. I froze for a second, then walked away. Yesterday, my dad made a joke about how “Sarah’s more excited to see you than me when she gets home.” I wanted to disappear.

I feel disgusting. I know this is wrong, she’s my dad’s partner, and she’s been nothing but nice to me. I haven’t done anything creepy like spy or make a move, but the fantasies are there and I hate myself for it. Part of me thinks she might feel something too because of the lingering touches and comments, but I’m probably just looking for signs because I want it to be true.

I can’t move out yet (saving up for college). I can’t tell my dad. I can’t tell my friends without them thinking I’m a perv.

What do I actually do? I don’t want to destroy my family, but I’m going crazy.

TL;DR: 18M attracted to dad’s 35F girlfriend who acts warm and maybe a little too friendly. Awkward close calls happening. Need advice on how to kill these feelings and not ruin everything.