Wedding guests drama

Chose what you want. Would you rather have your cousin there or his ex-wife? Just remember, at the end of the day it is your decision but, you do want to understand the consequences of that decision. I would personally tell your mom that your cousin being there on your special day is more important to you than having her friend. Decide which person you'd rather see that day. No one controls the guest list but you and your SO.

Invite who you want. This is your day.

The PPs are right. You decide who you want to invite. Do you want your cousin at your wedding? If yes, then respect his wishes and do not invite his ex-wife. If you don’t really have a feeling on it either way then go ahead and invite both and let them work it out. But do know that it may put a strain on your relationship with your cousin.

Going through something similar! My FH's sister just got divorced but we really like her ex-husband and have remained friends with him still. We decided at her request that we would not invite him so that she wouldn't be worried. You have to decide who would make more sense to have there. Your cousin is your family, so personally I'd probably invite the family over an ex-wife who happens to be a friend of your mother. But if you aren't close with the cousin and you are closer with the ex-wife, it would probably make more sense to have her there.

Think about which person you would rather have there, and don’t let anyone else persuade you otherwise! It’s your day

Invite the one you want. Invite them both, singly, if you want them both. Let them sort out which of them can be civil with the other present, and which can't. Tell mom to stay out of it. At some point it is good for a divorcing or divorced couple to treat each other with the civility we give to acquaintances, at least. It takes some longer than others.