One, it is good that he is slowly opening up to you. Keep letting him progress at his pace and you should keep seeing some good results.
Two: About the 22-year-old, there are goods mixed in w/the bads here. It is good that he is openly telling you about her. That is extremely positive as he is not wanting you to think negatively about the car share situation.
However, here is where you are at your cross-road with the redo w/BF. You will (and should) continue to have doubts about him as he was the one who was dishonest and strayed from you.
He will have to prove it to you that he is back and back for good, but human nature will always leave you to question.
How to handle this? I don't know. I would suggest being as honest as you can be w/the situation and how it makes you feel and why. However, you may not be in a place to do that right now.
It continues to make sense why people say adamantly that the piecing phase is in many ways more difficult than the left behind phase.
Hang in there and note the positives.
RTL PS - The mom in room thing is pretty creepy too.
