Well while I am unaware if this is a serious post or not,
Let's give you Op the benefit of the doubt and let us say that yes, I do take you seriously here, and consider your feelings.
Now then. I've had an experience of my own with an extraterrestrial, or alien.
Only with myself this was not in my mind's eye, and was seen physically by me.
No. It was not an abduction case. I was not probed or brought up in a ship- although I may have seen the ship as well.
This entity- alien, was but seven or eight feet from me, sitting in the passenger seat of my father's old broken vehicle.
Yes, I felt via thought a type of telepathic communication- as Rena described.
It seemed able to hear my thoughts, the thing that bothered me is I was not able to clear my mind at all around this being, I was not able to meditate and clear my mind of information as I've been able to do with other entities. With this thing, I tried and tried, and I could not stop my own thinking.
I heard a thought come through. The thought was "What do you know about nuclear power?"
I was very taken a back.
I answered via thought "Nothing. I know nothing of nuclear power..." and then my mind went into thinking, overdrive mode with- why the hell does it think I know anything of nuclear power? It isn't like I work at a power plant...
Next protruding thought- "Yes you do. You know something about nuclear power".
This alien like being was not gray, but brown in color, big shiny black eyes.
It never made a move toward me. Did not leave the seat, come close, or bother me in any way. But the feelings it left me with? Utterly indescribable. It felt evil, despite it caused me no harm you see? I've seen demons whom were utterly malicious in that they have caused harm, but this was something else. I find it very hard to properly explain to those whom have not experienced it themselves.
It felt invasive, pervasive, like an invasion of privacy being around the very thing. I was seven or eight feet away sitting outdoors on my front porch but the feeling of privacy invasion was so strong. I felt like I was being completely scrutinized.
Now having been through this, still surviving, but with a better understanding on how I feel about aliens, and the difference between the demonic, I can read your post and very well understand that this is in your mind's eye during intimacy.
With all due respect, first what is it you are seeing? You say they are gray? What do they look like?
They sound like gray demonic entities I have seen by the description of gray.
That doesn't mean they are or are not. But with a description of gray we've not much to go on.
What makes you think they are alien?
All that aside. Perhaps your mind's eye is letting you know of another entity that may exist. That's fine and well, but really now?
My point is, do not let such things bother or affect your time with your significant for intimacy.
Don't focus on the images during sex for God's sake.
Don't let such things interrupt or otherwise control your life hon.
Do not give your power away, to something external, that does not need nor deserve it.
Your mate needs your attention, not an image in your mind's eye of whatever it is or is not.
Easier said than done you may think? Not so hon. Ignore it. If I am able to ignore random imagery of things, so are you.
And I have had something similar- only my images were of grayish demonic entities which I've confirmed via someone else to exist as we've both literally physically seen them.
Nights and nights of my own time were interrupted by images of these things. This was in the same building where myself and the other individual actually physically saw them.
As for your mind's eye, it may mean you are able to sense non human entities around you.
But do not fall to fear, and certainly do not give the images any energy thought, or power.
Your focus belongs with your mate, love will prevail.
Ignore anything that challenges that.
All my love, support, and best.