You and Optimus Prime both love each other but don't want to tell each other. Both also feel the need for a little fun. (Y/N) gives in and goes to Prime's room' though he said no one is to enter. Before (Y/N) knows it, she's nude on Prime's berth, and the two are having a little fun.
Warning; sexual content

(Y/N)'s P.O.V.
It's been interesting working with the Autobots. It's fun being friends with them, but I didn't think I'd fall in love with an Autobot, add he's the leader. There's the obvious problem; would Prime — being the leader — even allow himself to be in a relationship with a human? Then there's how my family — or any human— would react to such information. Sure, the whole love is love speech, but does that apply if it's a human/ alien relationship?

I'd find myself daydreaming about how things could be perfect; I'd be together with Optimus, and everyone is supportive of our relationship. The last few days, I've been daydreaming about us doing it. It's gotten to the point where I want to do it, but I can't even if I finally told Prime I love him today. Though maybe that would help relieve the need, still, what if our relationship is frowned upon?

Today I've noticed Optimus is a bit off. Maybe it's the stress of being a leader getting to him. The damn cons have been very active lately.

From time to time, I hear groaning from him; I guess the stress is getting to him.

I sit with him as we watch a movie with several other soldiers and bots. I swear, along with the obvious exhaustion, I see his member. What the hell? Oh, let's add this is getting me to want him. The fact we're in the lounge room with others is the only thing stopping me from taking his pants off.

A little time passes before Prime announces he's going to bed, and no one is to disturb him. It's funny he looks right at Sideswipe when he said no one is to disturb him.
Are you doing some midnight pranks, Sideswipe?
I want to follow him, but that might seem odd even if I say I'm going to bed.

I wait for a half-hour before my mind is screaming, 'go to Prime's room.' I lie and say I'm going to bed.

Optimus Prime's P.O.V.
I try to get relief from this fragging heat cycle; finding our bipedal form helps a little, but it's still painful. Being near (Y/N), the femme I love, didn't help. I lay on my berth, trying to relieve the pain, unaware (Y/N) walked in until I see her (e/c) looking up at me. She study's me before climbing onto the berth. I smell her hormones. Her desire for sex is not helping me. I am the leader of the Autobots and shouldn't be doing this.
"I'm sorry," I apologize though it's clear (Y/N) wants this.
I shrink my bipedal mode down to six feet tall. This should be enough to be able to frag (Y/N) without using my holoform.

(Y/N)'s P.O.V.
I've never seen pink optics and considering what I saw earlier and Optimus' attitude, I think this means his sexual desire is in overdrive.
Well, at least I can convince him it's not rape if he thinks it is, even if I'm not screaming.

He removes a panel, and something I assume is their version of a penis sticks out, ready for fun. Though I didn't think Prime would rip my clothes off. His cold servos touching my (b/s) breasts feels nice. He massages them for a few minutes before moving on to fingering around my vagina. He knows we're both ready. Even though I know it's coming, I'm still unprepared when he penetrates. I thought I'd feel cold metal, but I didn't. I don't know if I could say it felt like a human's penis as I've never had sex with a human. Ev n if this is my first time, I know for certain Prime is being rough as he's thrusting, but I like it.
"Yes, Prime, fuck me!" I beg.
He keeps this up for a few minutes before collapsing beside me.
Did he seriously tire himself in to recharge?
His bipedal form reduced to the size of a human sleeping looks so cute. I stare at him for a while before going to sleep.

The next morning

Optimus Prime's P.O.V.
I wake up and discover (Y/N) next to me, nude. What the frag? To make matters worse, my spike is in her valve. I remove my spike, panicking as I don't remember what the frag happened.
Oh, scrap, please don't tell me I raped her?!
"I am so sorry," I apologize as (Y/N) wakes up.
"It's ok; you clearly needed it, and—."
"No, I took advantage of you!" I argue, "I fragging raped you!"
She silences me, "no, I choose to come here... I-I love you. I know this is so wrong, but—."
"No, (Y/N), it is ok. I love you. Now can you walk?"
"No," she says, thankfully sarcastically.
"Very well."
I play along and lay next to her. (Y/N) kisses me as I hold her close.