Pls Help! I had passionate sex with my father’s new wife and I can’t stop thinking about her

I’m an 18-year-old guy and I am in serious trouble right now.

My dad is 48 but his girlfriend is just 30. They got together some time ago and are now married.

However, I have always found her attractive and she has been leading me on too.

She’s been teasing me, flirting with me and running back to their bedroom n*ked after a shower, claiming she “forgot” her dressing gown.

I found a girlfriend of my own three months ago. She’s 17 and I think I’m in love.

My dad’s girlfriend had a chat with me over breakfast one day and asked if I would like her to show me how to put a condom on. I almost choked on my cereal.

She told me to go upstairs. She stripped me n*ked and showed me what to do.

The feel of her hands on my body was amazing and we ended up having s*x.

She said that I’m “big” and I think she wants us to carry on having s*x. I’d like that too but I am worried I might lose my girlfriend if she finds out.

I’ve thought of asking her if we could have a threesome with my dad’s girlfriend — she might learn from it as she’s very inexperienced — but she might think I’m stupid or just end things with me if she thinks I’m weird.

And if my dad finds out, he’ll leave his girlfriend and will surely hate me.

I love my girlfriend but I can’t stop thinking about my dad’s lover. What should I do? Oh my God!!!