Your best bet is to just have the conversation about what you both want. If you want a relationship, tell him and see what he says. If he wants to keep it as FWBs then you have a decision to make. You either continue as is even though you are developing feelings for him (which could be very hard and painful) or you move on to find someone who wants a relationship in the same way you do. Most people don’t have these conversations because they fear the other party’s answer and having to make a choice, but delaying it only causes more pain down the road. Have the conversation and see what happens.

Best of luck!
~Jodi