u/HappyTaste1333

I’m a 25F getting married to my fiancé, Nelson (24M), early next year. We recently booked our dream venue on a beautiful lake, but it has a strict capacity of 125 people, and we cannot go over that limit.
I have a large family, so most of our guest list is family. Nelson has a smaller family but many friends. I’ve only invited four of my friends. We also each have eight people in our bridal party.
Because of the venue limit, we decided there would be no automatic plus-ones. One of Nelson’s groomsmen, Mike, received a save-the-date with only his name. Mike is Nelson’s oldest friend, and we absolutely want him there.
Mike’s girlfriend, Susan, and I actually went to high school together, but we were never close. I’ve been with Nelson for two years, and I’ve only seen Susan twice during that time. We don’t have a relationship.
Apparently, Mike told Susan she wasn’t invited, and they’ve been fighting about it for 2–3 weeks. From what I understand, Susan has essentially given Mike an “me or the wedding” ultimatum.
Susan has apparently asked why my brother’s girlfriend, Katlyn, is invited if there are no plus-ones. Katlyn is one of my bridesmaids, and I’m very close with her. She isn’t invited simply because she’s my brother’s girlfriend; she is actively standing beside me in the wedding. My brother is also planning to propose to her before the end of the year, so she may be my future sister-in-law by the time we get married. My FMIL has also asked why she was invited due to Nelson’s 18 yr old brother’s gf not being invited, even though we have no relationship with her as well.
There are a few other exceptions to our no-plus-one rule. My best friend’s boyfriend is invited because Nelson is also very close with him and we regularly spend time together. One of my cousins in the bridal party may have her boyfriend invited, depending on their relationship. Another groomsman recently got married, so his wife is obviously invited, and I’ve spent plenty of time with her.
The common denominator is that these people either have an established relationship with one or both of us or are directly involved in our wedding.
Susan was actually on our B-list. If enough people declined and we had room, we planned to invite her.
I understand why people are telling me to just invite her to keep the peace. I absolutely want Mike at the wedding, and I don’t want him to feel like he has to choose between his oldest friendship and his girlfriend. However, I’m also worried Susan may still be upset or refuse to attend because of the tension this has already caused.
If we had unlimited money and could have a 200+ person venue, I’d happily invite everyone. But we’re two young adults trying to make a wedding work on Long Island, and we have a hard 125-person limit.
So, AITA for not inviting my fiancé’s groomsman’s girlfriend when we have a strict venue capacity and no relationship with her?

I would also like to add that Mike is not the best man. Just his oldest friend. His best man is a friend he’s known for 4 years.
The two times we did hang out with Susan and Mike together she treated me like dirt but I left that out due to the character count limit. We went to a hockey game and she didn’t talk to me at all. The second time was for mikes birthday and she had most of her friends there and some from high school so I went over to make conversation and it was like pulling teeth and super awkward. Also didn’t talk to Susan for the rest of the day. I ended up following my fiancé around like a little puppy dog because I didn’t belong. Which is more of a reason why Susan is invited because she makes me feel uncomfortable.

Along with the large bridal party everyone keeps mentioning. It is that big bc of my fiancé. I would’ve been happy with 3 bridesmaids (my 2 sisters and his 1 sister) the rest of the fill ins are his friends so I had to accommodate my cousins and two friends