Three I know the guy is playing her I see the tricks
It doesn't matter what he's doing. Your wife is no longer emotionally invested in you. When another man becomes more interesting to her than the man she's currently with, then it's finished. Getting her to regain interest in you becomes an uphill battle that you will likely lose. Your marriage is over.
The best thing you can do before you file for ANYTHING is sit down with her, and
calmly sort out who gets what, what the child visitation arrangements should be, child support payments (if any), what happens to the family home, etc. You can get a separation agreement done up by a reputable website for a small fee. Get EVERYTHING in writing before you start fighting in court. The more you have in writing, the more leverage you have and the less likely she will be able to alter things in the agreement.
This is exactly what I did with my wife when I ended the marriage. It was a fvcking life-saver. While sorting all this stuff out, you CANNOT get emotionally heated or bring up the issues that caused the marriage to fail. You NEED to focus on getting everything sorted out in order to protect your investments. The both of you may need to compromise on things, but if you avoid getting emotionally heated over the issues, you CAN get it done, and you will be thankful that you did it before anything goes to court.
You need to think of it this way... She wants out of the marriage, and you should want out of it for the sole reason that she does NOT want to be committed to the man she claimed "til death do us part". That's what marriage is supposed to be; "til death do you part". So she fvcking lied, had a kid with you, and has let her interest stray elsewhere. You do NOT need to be married to a woman who is an unfaithful, non-committed liar. You should want out as well. You are now left to fend for yourself, and EVERYTHING you do up until you make the separation agreement official is going to affect the outcome of your future.
Work on the separation agreement WITHOUT lawyers. All the lawyers will do is drag out the negotiations about who gets what and eat up your money. The both of you should be able to figure out what you want to walk away with together. If she gets heated, you need to calm her down as opposed to adding fuel to the fire. You need to take charge of getting your assets and your visitation sorted out. If you don't, the courts will decide what's fair and you'll likely get screwed.