Does this count as rape?

When I was 19 I had a boyfriend who was bipolar and during his depressive streaks it would be very difficult to be around him. He would create such a dark environment and would want to be by himself, so whenever he was like that I would just leave him alone until he came back up and would be happy again. During this time my own wellbeing suffered as I would worry about him constantly.

But one time I went to visit him at his parents house in a different city for a few days, where I stayed in his bedroom with him. During this time he got pretty low, and there was only so much I could do to not be around him like he wanted, as I had nowhere to go. One afternoon we were watching a film in bed (in an attempt to keep his mind of his depression), and he got angry at me because I let something slip about the ending. He demanded we turn off the film as there was no point in watching it now.

Feeling helpless at how to help him when he felt like this, and also trying to explain that the film wasn't ruined (the information I gave him wasn't important to the storyline), whilst also trying to be sensitive to his frame of mind, I did as he said and closed the laptop.

I remember this bit really well, as I think I must have thought back to it a lot. As I leaned out of the bed to put the laptop back on the floor, he turned in bed and penetrated me from behind. I was still half out of bed and definitely wasn't in the mood to have sex at that time, feeling guilty and confused at his sudden anger at me. I looked back at him, and didn't try and get him to stop, because I felt like I couldn't. I turned my head back round and looked at the floor and let him continue. I remember feeling like I wanted to cry during this, and knowing that shouldn't be how sex with my boyfriend should feel, but I told myself that I couldn't cry as that would upset him.

I always knew that what happened wasn't right, and that I should have told him to stop. But I recently learned that rape is defined as any sex where the person who didn't instigate it doesn't want it to happen. I am not going to start saying I was raped, but I'd like to know for my own sense of self if what happened was as bad as I felt it was.

Thanks for any help.