Why would your FWB say he has a girlfriend and yet spends 2-3 hours texting you with only 1-2minute breaks?

We text nightly and he initiated the texting this week. We had not texted like this in 2 months.This is the second time he does this. Last night my response was the same as the first time. I said good I'm happy for you. You deserve to be happy....his response was I 'm tired talk to you later. We have been FWB for a year and we work together. What gives?