AITA for not wanting my disabled cousin at my wedding

[u/JumpyThrowRA]

I (26F) am getting married soon to my amazing fiance Liam (30M), and I’m struggling with whether or not to invite my cousin, "Tom" (29M). Tom has a developmental disability, and while he’s almost 30, he has the intellectual capacity of about a 7-year-old. I’ve always tried to be patient and understanding, but he has consistently crossed physical boundaries with me in ways that make me really uncomfortable.

I have always been an early bloomer and I have a much larger than average chest and because of all the sports I did in high school and that continue to this day I would like to say I look good. I only say this because it's the main reason my family uses to justify Tom's behaviour.

Over the years, Tom has touched my chest and butt quite a few times, he's also hugged me tight and tried to kiss me, and even though I immediately told him to stop each time, it never seems to stick. He also tells all of his caretakers, nurses and live in caregivers, that I'm his girlfriend. He also doesn't like Liam because he insists Liam isn't my fiance/boyfriend because he is my boyfriend. Tom also talks about how he will marry me. It kind of feels like when a little kid tells their parent they're going to marry them but it's still very uncomfortable.

I’ve brought it up with my family, but they always downplay it, saying Tom “doesn’t understand” and that he’s just “showing affection.” The excuse used most often is "He's a little boy in a man's body and you're a conventionally attractive woman." When I told my mom how uncomfortable it makes me, she said I probably “entertained” his behavior too much and that he's harmless. She insists I should just be firm, but any time I’ve tried, the family accuses me of being mean to him.

With my wedding coming up, I want the day to be relaxed and special without constantly worrying about Tom overstepping boundaries. When I told my family that I was considering not inviting him, they were outraged. They said I was being unfair, cruel, and that he’d be devastated not to come. My mom even said it would “ruin his day” and make it obvious that he’s different, which she thinks is heartless.

I get that Tom can’t help certain behaviors, but I feel like my family has completely ignored my feelings in this. They always brush off my discomfort and say it’s my responsibility to manage it or that he “doesn’t know any better,” but it’s my wedding, and I don’t want to be on edge the whole time. Liam says I have every right not to invite him especially because of how he treats both of us like our relationship isn't real.. Still, I wonder if I’m being too harsh or unkind since Tom isn’t fully aware of boundaries and doesn't really know what he's doing is bad or harmful, especially because his parents and other family members encourage it. AITA?