How do I handle this?

 So, SO was kind enough to put my cat down for me and be there for her and all that good crap seeing as how I was in no condition to do it and I did not want the last moments of her life being with total strangers. ETC.......

In the time this is all going down my other 13yo cat, is having trouble chewing his food. I have known he has needed his teeth cleaned for a while, but the quote has always been 400 dollars and up. So immediately I start thinking omg, he's finally gotten to the point he has an abscess!! The first day I got a chance after everything with Punkin and the holiday weekend was over I call the vet. Background info b4 continuing: he does NOT do well going ANYWHERE. He pukes all over and cries the whole time unless I hold him (not a great idea trying to drive like that either)

So, also let me throw in one other good thing about SO b4 seeming to bash him : our anniversary was last Wed and he did so amazing I was very impressed and didn't think he had it in him. He had 3dz. roses delivered to my job!!! Bought me a very nice coach purse all on his own just guessing to pick it. Yes, so nice and thoughtful so far right?-----

I asked him if he could help me with taking 8ball to the vet on Sat. 10am.The first avail appt. and his response was "I don't know"  I'm thinking uhh,kinda important considering I just had to put one down and don't want to do it again because an abscess can spread rapidly to the heart and brain. His reason was he got a text from his friend that he's known since H.S. and his daughter, which is SO's god-daughter, is having her 8th birthday party!!! Response was not we'll work around it, it was flat out IDK! I even reminded him how important it was and that I could use his help with him because he is such a handful, then asked if we couldn't just go to see her after the appt and he again said IDK! At which point I got mad at him and asked him WTH! He proceeded to go off on me about how he's sorry that HIS FAMILY has plans, I've known about his teeth going bad for a long time, and now all of a sudden everyone's just supposed to drop what they're doing and don't I dare throw up in his face about losing MY cat of 15 yrs because he was there during it just to comfort me. He does,does ,does for me and all he ever hears about is what he doesn't do for me! oh yeah, and when I told him his IDK response was not good enough he stated that he is tired of bowing down to me.

How can such a seemingly good man turn into such a jerk? I am honestly baffled. He can be so great and caring and then turn around and be a total jerk. I didn't ask him to take her and be with her while they put her down, he freaking offered!!!! WTH is with the whole HIS FAMILY  stuff? What have I been doing for 3 yrs, playing house?

How do I handle this? He has many great qualities but this is blowing me away! I don't want to fight with him and I need to know what I should do.