@lukester09 Sounds like it's time for some limits. "I am not going to nurse you here. You are a big boy, and you can wait until we get home." "Okay, we are going to be done now. We can nurse again at naptime."
He will probably balk and push back and be mad at you. But look, it's
good and necessary for them to learn to deal with boundaries, disappointment, frustration, all this kind of stuff, and this is a reasonable limit to set. Hell it would be completely fine to go ahead and wean him if you wanted to. (Edited because what I originally said came out bad -- it's fine to transition off nursing at any age, and he's old enough where you don't need to compensate in any way other than maybe a few extra calories.)
Try to work on not taking his responses personally. (I have a 12, a 10, and a 2, and I am still working on that!) Learning a new thing is confusing and hard at first. He will direct his frustration at you, first of all because you're the one who imposed the boundary, and also you are mom and where else can he direct his feelings? So, knowing this, you can validate and express compassion for how hard it is and how big his feelings are, without acting like you did something wrong. (Even if your mom-brain is screaming at you that you did something wrong. You didn't. Brains aren't always right.) And be his big solid comfort object.
It really will get easier, with practice, to not feel like shit
By the way I am typing this comment with a nearly-3-year-old nurse-napping on me, so I am really hella lazy and permissive with the nursing. (We don't night nurse because of dental hygiene. Nurse, then brush teeth, then go to sleep.) A few months ago, I realized I was doing her a disservice by always giving in and nursing her when she was upset or hurt. (I really should have realized it earlier. But like... my kids take turns being the neediest pain in the butt, and it was some other kid taking up most of my energy. I don't even remember which one or why. Ha.) She was using it as a crutch rather than learning emotional regulation (co-regulation, that is. Sitting with me while we feel the emotion and then let it pass). So I had to be like "we are not going to nurse every time we are upset. We will be upset without nursing. I will nurse you at naptime," and boy did she think I was the evil mom from hell. But it passed, and she's fine. Growing up is just hard. Good luck!