faking an orgasm

So my boyfriend and I have been together for almost two years and he's never been able to make me orgasm during sex. Last night we were getting into it and he kept asking me to cum for him and so I tried but obvi I couldn't. So I ended up faking it at the end which made him cum too and it's all he's been talking about. Should I just tell him the truth or let him believe it?????? Help please