I'm Mean and I Dont Realize It and I Dont Know What to Do

WARNING VERY LONG

So, it was made aware to me that I am mean. I've never meant to be mean and the things I say to my friends and family are things that I'd want said to me in that situation. Basically, I treat people how I want to be treated (the golden rule). I was told growing up that if you follow this rule then people will like you. I do nice things for my friends and family and go above and beyond for them. I support them in their times of need and provide a shoulder to cry on. I put up with alot of abuse from them because my love for them trumps temporary anger. I feed them, will provide a roof for them or a ride for them, I'm just there and do everything possible to make sure their lives are happy even at the expense of my own comfort sometimes. I thought I was doing everything right. Apparently I'm not. I'm honest. No, not, "Wow you look really ugly in that!" honest, but, "I dont appreciate when you do (insert undesirable trait or action here) and although I love you I really wish you would change that." or, "I dont appreciate you projecting your negative traits on me please stop." I'm always polite about it. I've tried compliment sandwiches to no avail and I tried just being quiet which enrages people. I tried lying and hated it. I tried omitting the truth but they saw right through it. I tried to even make new friends but it doesnt matter. It isnt them it's me. Idk what I'm doing wrong. For example, my stepmom had just had my little brother (20 years younger than me and cute as a button) and during her baby shower I hadn't seen her in like 3 months. I've never carried a pregnancy to term so when I see a large belly I see it as a good thing as the baby is healthy so I thought I complimented her by saying, "Wow you've grown alot! The baby most be very healthy! Congrats!" I then smiled at her and she looked at me quietly then proceeded to tell everyone I called her a fat cow and didnt talk to me again until my brother was born and i visited her in the hospital and she is still very cold towards me. She is a really sensitive person so while i was very hurt i didnt think i really did anything wrong. Okay fast forward to a car ride where i was picking up my sister. My dad was in the car with me as it was a 3 hour drive both ways and he was worried. They were ranting about cheaters mindsets and how awful they are and i said to my sister, "Didnt you cheat on most of your boyfriends?" I swear I didnt say it to be mean i just had the thought occur and said it. I didnt think she would mind as she can get very mean when she wants to be so i figured she could take honesty. She said i was rude and promptly changed the subject. Then i had shared a post on facebook off tumbler that said something along the lines of, "It makes me sad that boys think they cant wear dresses out of fear of being picked on. If you want to wear a dress and get picked on then roundhouse kick them put on the dress and voila...you're wearing a dress." A comment below it said something about it being used as an argument against men who want to also hinder women from wearing pants. Well my friend went off. He posted in all caps about how sexist I was and how no man ever has tried to stop a woman from wearing pants. (idk where hes been but he is a very sexist man himself and quite often posts antifeminist posts and posts about how much he hates women then in person to me on multiple fronts he also ranted about trans people, nonbinary people, poc and basically anyone who is different from him and justifies it by saying he has a trans aunt and a bisexual girlfriend who both tell him that he is wrong all of the time). I asked him to please remove himself and his negativity off of my post and figured it was done. He then says that he has no negativity and hates no one but sexist women like me and that he loves everyone. I snapped because he has bothered me alot about my posts that support women, LGBTQ people, poc and yes, men. I told him he was filled with hate against (Insert all groups listed above) and that I have only ever fought for equality and have never had anyone but him call me sexist. He screamed i was blasting him on Facebook and spreading lies and that he was going to spread lies about me. I said that if he didnt agree with me that he could kindly unfriend me as my life is too short for negativity and conflict. I then tagged my friend who is very liberal and asked her opinion on the situation and she said I had no right make accusations like that without proof. If you literally clicked on his page his hate speech would be all over the place and my first hand accounts were proof enough for me. She didnt bother to look and I was told I was a mean person. He continued escalating so I simply blocked him. I'd been meaning to end the friendship anyways but still deeply care for his girlfriend who I'm closer friends with so I didnt want to hurt that relationship. She hasnt made any comment at me that says I've hurt it so idk about it but I hope I didnt. I've also had people give unwarranted advice on multiple occasions to me about how i dress etc and i always say, "While I respect your opinions and take them with a grain of salt, I enjoy the way I dress/do something and dont plan on changing it anytime soon." They take it as their opinions dont matter and it's almost like they expect me to adhere to their "advice" 24/7. I'm obviously lacking something everyone else has but, idk what. I dont like lying or being fake and I dont understand what I'm doing wrong. I use tact and I bite my tongue ALOT but sometimes I just dont catch it and I feel it effects my being able to make friends. How do I make better friends without compromising who I am as a person? It seems people only want to tell you how to act or tell you their opinions but never like it if you're honest about your opinions or observations with them. I'm so sick of being lonely though and feeling like an outcast. I guess I have serious foot-in-mouth syndrome. What do I do?