How to ask your fwb could it be more???

I like my fwb more than what it is. Him and I have been messing around for about 18 months now. He gets jealous about things and so do I but it's going nowhere. He blames it on working 3 jobs so he only has email amounts of time for me. How can I ask him what its going to be, if he wants more, I don't want to get more attached than what I already am. Hey a simple text idea would be appreciated. ThAnks girls