Getting into his facebook without changing his password?

[CαяOlιηα]

I don't want to hear about how it's illegal because right now I couldn't care less.
I have a strong feeling my bf is talking to girls on facebook. He's very secretive and has deleted me from his friends and won't accept me. Each time I have gone through his phone without him knowing I have seen girls sending him hearts and him saying he misses them and he quickly grabs his phone off me and now has a passcode on it and takes his phone everywhere with him.

First of all, if I wanted to reset his password I can. I clicked forgot password and guesses his secret answer and it took me to the next step to reset his password but he will know straight it's me 100%. I'm itching to do it but that would be the end.

Is there a way I could get into it without changing his password? I'm desperate to do so. Anything? Thanks!