Most Helpful Guy
Well, it's not a good way to test your boyfriend like this, because it shows that you distrust him in some or many ways and that is not a good sign at all. What you are doing is wrong.
However coming back to your testing tactic, yes he does seem to show interest in the other girl ( which is you texting as other girl), so from your test, I would say he has failed your test or is failing your test constantly which is also not a good sign.
The fact that you say he is lying is also not a good sign.
Most Helpful Girl
He's different because you violated his privacy, once you've done that there's no going back. He hasn't forgiven you and he's still carrying on messaging other girls behind your back. I've made this mistake when I was younger and I quickly learnt never to do it again. It ruins your relationships. If your gut feeling is that he's going to cheat he probably will. Our instincts are more accurate than we give them credit for.
Now you have him lying to your face when you confront him, he still messages them behind your back. You have more than enough evidence to leave him. Do it before he actually does cheat on you which may only be a matter of time. All it's showing him is that you don't value yourself highly enough to not be disrespected in such a way.
This is not going to get any better with you checking his phone or with lying to him to 'catch him'. Leave and don't look back.