yellowdoxie, I'm so deeply sorry this has happened to you. We all are, it's just one of the worst things a person can experience. My hugs to you.
I'm going to be blunt here, it's my nature, and I like to cut through the emotions to a more solid platform of action because....the emotions cycle rapidly or just deepen - they're not a reliable basis for knowing what to to think or do. It turns into a swamp.
First of all....your wife has NOT been honest with you. She's been involved in this relationship, to whatever extent, for whatever extent, for whatever reasons, and you don't know everything and you probably won't at this point. She hid this growing relationship from you, which you could sense that something was happening, she has actively pursued this, knowing she had to hide it from you, so she has been ongoing deceitful, she tells you over and over that she doesn't know why she is doing this....that is a LIE. I know why she is doing this. She's doing it BECAUSE SHE WANTS TO AND HAS CHOSEN TO. And those are the only reasons that are important. Everything else is window dressing and at some point, she's probably gonna start blaming you, because that's what they usually do. You would be amazed at how unoriginal most of these cheaters are. And that is NOW what your wife is....a cheater. So, that IS your answer. She wanted to do this, she chose to do this, and she has done it to whatever extent, and she will probably do more. She hasn't said she won't, right? She hasn't said she's gonna end this, right?
"Time and space" means she wants you to leave her alone so she can pursue this affair in peace. She's telling you to back off and let her do what she wants under the guise of "oh, I don't know why I keep writing sexual stuff to this guy and planning sex with him? how could I possibly know that!....give me some time and space!"
That is complete and absolute bullshit and you need to get angry. Not just sad, devastated, hurt, rejected, all that - you wife has been actively plotting against you and your marriage and your son with another man. GET MAD.
What does get mad mean to me? GO TO A LAWYER ASAP AND FIND OUT WHAT DIVORCE LOOKS LIKE FOR YOU AND FILE. YES, FILE FOR DIVORCE. As soon as you can. And then go home and TELL HER you have filed for divorce. Tell her you WILL NOT share your wife with another man, that she can either have you or him but not both. She has to decide and she has to decide NOW. You'll find out what she's really like - even if she says she loves you - well she probably loves her brother, the dog, chocolate, and white clouds - saying she "loves" you doesn't mean a goddam thing. SHE DOESN'T RESPECT YOU BECAUSE SHE DOESN'T THINK YOU'RE GONNA DO ANYTHING ABOUT IT.
Well. DO something about it. GO FILE FOR DIVORCE. You don't have to go all the way through, you could pull it at some point if you think she genuinely means it and recon is worth while (personally I don't) but it gives you the head start of taking action, setting your boundaries and limits and what you will and will NOT put up with. Don't put up with this behavior from ANYONE. You can always lose weight, improve yourself and BELIEVE ME, many other women would gladly have you. That is the truth. You don't need this woman, there's ALWAYS somebody else, especially for a man. If you want it. Don't take shit off anyone and that's what she's tell you to do with this "I don't know" bullshit. People will always hand you just as much shit as they think you will take.
Also, get an STD test. Keep in mind as well...this may not be her first rodeo. I'd like you to start loving this woman....a whole lot less. Take her off that pedestal. You haven't cheated - you ARE the better person. She is full of shit. TAKE ACTION! P.S. You might start officially recording all your transactions with her - now that trust has been broken, you don't know what else she is capable of. I have known cheating women to accuse their husbands unjustly of abuse or being afraid of them - talk to the lawyer about this. BUT....get to a lawyer and start the divorce. It's scary....but you need to take action. Time and space is just you being a chump, respect yourself and others will too - it's contagious.