Let me preface this to say, I’m not bothered by getting married, I’ve been married, it didn’t work out. I would have got married for him, but I don’t have a burning desire.
But my boyfriend had been keen since we met. Often asks me in passionate moments, talks about it rationally, has said he would love me to be his wife, what a proposal would be like etc.
My divorce went through this week and all of a sudden he’s had a change of heart. He said last night, ‘I’d love to be married to you, but it probably isn’t worth spending thousands on a ring or a massive wedding’ - I nodded along, but it was a massive shock as it was such a change of heart.
Where did that come from? He doesn’t want to marry me, and probably never did, did he? 
YABU - he did/does still want to marry me
YANBU- he clearly doesn’t and never did want to marry me.