Hi Sharon!
This sounds really weird, but check his teeth. I had a female rat
with weepy eyes and it turned out her teeth were too long. The top
incisors are very short and should overlap the bottom incisors by
only one or two millimetres (they shouldn't be too close to the roof
of his mouth). The other possibility is that he got accidentally
scratched by his cagemate when they were playing or maybe he got
something in his eye, like litter dust. If that's the case, washing
the eye regularly should fix it.

Kind regards,
Megan