Welcome FUBAR - You will find a wealth of knowledge here. You will also find tons of support.
The way things are going right now with R, no they won't get better, and no you won't build trust. However it is possible to do that, and get to a point where a M is healed from an A. It requires both partners being fully commited to it, and working dang hard to get there.
Your wife has done nothing to and is doing nothing to heal from this. I would even bet that she has a secret phone, &/or a secret email and is still communicating with this guy. Right now she gets the best of both worlds, a husband and a boyfriend. One who makes her feel safe, and secure, the other makes her feel sexy, exciting, and whatever else she is getting out of it.
If you have not figured out what you need from her to successfully R then you need to do this. You need to sit down with pen and paper and make your list of requirements for R, along with consequences, and be prepared to follow through with them.
You have done well to focus on you and get yourself strong. This is very important. You should also do a few things that every BS should do, if you have not already...
See an attorney, find out what your rights are, and what would happen should you choose to S or D.
See your Dr, request STD testing. If she is having an A who knows what the other guy has done, and is doing....You have to protect yourself for you and your kiddo. Make sure you are eating, drinking, and sleeping if these are hard and not being done, talk to the Dr about a little pharmaceutical support temporarily. It's ok many of us have had to do that to get us through.
The fact that she wants to pretend all is well and back to normal is a huge red flag for me. This is what a lot of WS's do when they take their A underground, and definitely don't get the damage they have caused. I would encourage you to spy a bit, yah it sucks, but you need to verify that she is being truthful now. She has proven herself a liar, so it's just being smart, and protecting yourself at this point.
keep posting, keep asking questions...
((((and strength))))