I have an issue with the "slept with" bit.
What if you always leave before falling asleep?
"The middle one is clear, but what's the difference between "penetration with a penis" and "any sort of penetration"?"
Fingers and toys are my first guess for what else could constitute penetration.
On topic, my count's four, soon likely to be five. I've had more luck with duration over number of partners, and I was a bit of a late bloomer. 
Edit: One more if fingering counts.