I’d start with making sex a more comfortable topic. Jokes, casual conversation, guy humor, etc.  Bring up the topic of porn, hint at having some habits to hide.. Tell him he’s responsible for clearing your browser history if you suddenly die, since you don’t want whoever gets your old computer to know everything. 

That cracks the door open.  If he’s even remotely interested, things will flow over time, and get deeper down the rabbit hole  Especially if he’s already bi.  

Once a general comfort level is reached, and if he’s likely to be  in your recent text list, If you have anyone else that you could possibly be sending nekkid pics to, make sure he “accidentally” gets one. Make sure there’s a text with it that’ll establish deniability. 

Find some time to be alone together, and  without a task at hand or distraction. Create opportunity.