My boyfriend stole from me?

I've been with my boyfriend for three years and he has never done this before or been this kind of person.

He's terminally ill and can't work right now so he asked me for 40 bucks to borrow for gas and prescriptions.

I said yes but that I need it back that night to pay a ticket off. He agreed saying he would have his parents pay me back.

Well this happened on Thursday and I still haven't gotten the money back nor can I get a hold of him...and it turns out he pulled $60 from my checking instead of the $40 and continued to let me believe he only pulled $40!

I'm so heartbroken. I just don't understand why he is doing this??? He has neve ever ever stolen from me or been a dishonest person. We're going o three years together and I'm just stunned