I understand that this is a reconciliation forum. And the advise offered by MWD and many of the posters is wonderful when your marriage needs help.
Its not wonderful advise when you are being abused, gaslighted, or betrayed. (Although there are some codependent and masochistic people on here that will say otherwise)
Cheating is a form of abuse.
But he did not just cheat on you. He left you and chose another woman. He is now writing sentimental BS to you so that he can keep you on a string. He wants 2 women fighting for him. That serves his ego. And if hes going after women that young, its all about ego.
Dont go back to him. This woman has done you a big favor. She took an uncommitted and disloyal partner. She won no prize and you only lost someone undeserving of your loyalty.
If things dont work out between him and 25 year old, he will come back to you (hes setting it up so he can) and he will do it again. Cause that is who he is. Our forums are filled with people whose spouses returned only to eventually do it again.
Do you want to be back here older and with less options? Maybe next time he will plan ahead and wipe out the assets. He will be more experienced.
I know. This is hard sh!t to accept. It forces us to grieve. And no one wants to grieve when there is hope. No one wants to face up to the fact that the person they married was not who they thought they were. Its hard coming to terms with it. Its hard coming to terms that the person you loved and trusted is really a narcissist. Or sociopath. And trust me they are.
MLC is BS. Its a term that people that are capable of love use to project onto their spouses because they cant comprehend cruelty. They need something to sxplain the "how could they"
Write him back only when it concerns logistics. If you say "if this is what you really want" you are giving him all the power. Those few lines tell him that you are waiting for him. They show him that you are willing to be 2nd choice.
These are my thoughts.
Get into a stronger place emotionally right now. Build a new life. Put yourself in a position of strength.