So he dumped the "I'm not sure if I love you" line before Christmas, which probably left you scrambling trying to 'fix' things, while he was having sex with another woman. Now that you have found out about his secret liaisons he suddenly "really does love you and wants to make it work".
The truth is; he would never had told you what was going on had you not found out. The truth is; the "I'm not sure if I love you" line was an excuse so he could distance himself from you so he could enjoy his secret liaisons without the guilt. The truth is; this isn't out of character for him, it's just a side of his character you hadn't witnessed before.
You have just boarded the post discovery roller coaster, what you feel now is not what your gonna feel tomorrow, let alone in the next hour.
It sounds like the "I'm not sure if I love you" line before Christmas has more affect than you realise. Then the origin of the uncertainty was unknown but that threat now has a name and body parts and you may be avoiding searching questions in an attempt not to drive him away.
Despite what he's done you're not suddenly going stop loving him or loose the urge to stop protecting him and his reputation. However, don't let friends or family thinking less of him be a barrier to getting support, he is responsible for his reputation, not you.
His remorse and devastation at what he has done could be genuine but you can't be sure of that, the presumptions of truthfulness when it comes to this man has now been suspended.
Why is him not going out a sign of his determination for not letting this happen again, does he really need to do this to stop himself falling into random vaginas? Why is him temporarily leaving not on the table? Are you afraid that he would view this as just cause to sleep with other women, if it is, then despite what you say deep down you don't trust him.
Right now you're desperate to relegate his infidelity to some kind of abhoration. Naturally he is more than willing to go along with this because it has less impact on himself.
You don't have to LTB but if you really want to save your marriage than honesty is required on both sides. If the cost of saving your marriage is a life of living in denial then that is a high price.