Should I be angry that my best friend was having sex with my son?

Right or wrong, its none of your business. Drop it already. You can drop your friend also. Mommy, let your son live his life.  Your husband is right.

If they were both consenting adults then it is none of your business. You don’t own either of them and they are free to do what they like. You are also free not to be friends with this person anymore, but that is on you, not them.

If your son is not an adult, then it is a crime and I would report them. Speak with your friend and ask why she did it and if the reason is not acceptable you can be unfriend with her. 

Your friend is 32 and your son is 22, and they are both adults. They can have sex with each other any time they want to. They don't have to have your permission or your approval in order to do so.. 

I'd be miffed if it was going on for a while, but really why be angry? Disappointed I suppose in the both of them if it's been going on weeks or months and you just found out. Hard to know who you might fall for.

no be happy for your son

I think its a really uncomfortable situation to be in. I know age is just a number when your over the age of concent. But I personally think its really odd for a 32 year old woman to be having sex with her best friends 22 year old son. I honestly think they both got a thrill out of it, knowing that it felt sort of wrong. You have every right to feel angry and I think its more frustrating to know that your husband is not on your side. At the end of the day, you will always think of your son as a child, even if he is technically speaking an adult.