Honestly, in your situation, I wouldn't.
Not because he'd tell everybody, although he probably would tell his friends, but because suddenly you're introducing stage issues into sexual performance. Being a male porn star is difficult, to say the least. I'm assuming this is amateur, but even so, being watched can really mess with people's heads.
Besides, four months in seems a little early. Introduce him to the fact that you do this when you're ready to do so, but don't involve him unless you're sure he can handle it.
Yeah, seriously. DONT tell him. He may get confused, jealous or feel intimated by your choices. The economy's tough and he may not just see this as just a means to make money. He may take it to heart. Wait. And try to get off that site eventually if you can!
Yeahhh, maybe you need to break the news that you work on a porn site to him first before you think about making money out of him? His reaction would probably be a good indicator of whether he'd be comfortable getting involved too.
It helps to read the question: she makes it clear she hasn't been having sex with other guys on film.
It ain't all that uncommon. Many of the leading porn stars were married - while they were porn stars. If their spouses were okay with it, then it's not cheating, period.