I must say, I did wonder about the 180 thing, or something along those lines anyway. I don't think the 180 quite hits it though. But I don't know how to put it into words, other than if you think you are going to lose something then you look after it better. If you feel you have to compete with others (in the sense of others may find your spouse attractive and that you want no one else to be as good a partner as you) to ensure your spouse stays with you and never has any intention of straying then you make a lot of effort. It seems maybe he has never thought that he has to work to keep you?
Also, he is only 1.5 months out. That is not long. And your head is in a mess. Time will help. I found the 3 month mark was a turning point. Then the year mark. So much better after that. Though mine did not do all I needed to fix it. I did the heavy lifting. He just gave the love and told me to 'trust him'. Ultimately we finished.
In my previous relationships, 7yrs & 11yrs when the passion died, I think it was basic incompatibility. The love just wasn't there. I found who I thought was the one, my soulmate, total chemistry, total compatibility, and found myself here on this forum. I am gutted we are not together anymore, we both still love each other very much, but there was just a few fundamental issues that could not work for me considering his infidelity.
Only you know your relationship. Though I fear that if the lack of passion is mutual, then it will take both of you to want it badly in order to restore it. I hope he also has that desire.
I think there is a lot to be said though in having much passion with someone you don't want to lose. That (losing them) being a real possibility (in as much as they are very special to you, and attractive to others) means more value placed on the relationship. As I get to the end if my post I think the 180, in a very positive and loving way, would be good. Do things for yourself, get interests outside of him, look after your appearance, make him wonder what you are doing and why. If he asks, you are making positive changes in your life in order to counter the crap he has thrust upon you. This may well wake him up. In fact, it probably will. And if it doesn't...you will feel a whole lot better regardless.