Should I feel the way I do?

I can’t help but feel completely embarrassed and ashamed. I finally had sex with my boyfriend of two years (we are almost to three years together) and I had made sure to get condoms to keep in my night stand just to be prepared. I’m not on birth control yet, i will be but for now i am relying on condoms and the pulling out method (both used each time.) My older sister found two of my condoms this morning and decided to yell at me about how much of a slut I am and how she thought I was better than to sleep with someone who I have not married yet. She’s 22 and I am 18. Anyway, she’s had sex many times and she’s not married, so I don’t understand! I get that it can be part of her religion but she shouldn’t treat me so bad. She’s always trying to find ways to hurt me. Plus, I’ve only had sex with him once so far! I do not regret it and I love him. But why do I feel like I’ve disappointed her when she’s never really cared about my life? I wanted to yell at her and tell her off. But i chose to be the bigger person and ignore her. I know I am not a whore or a slut. I wasn’t having sex with a stranger or multiple. I just wanted to spend time with my boyfriend and it lead to me losing my virginity. And I was ready! It was my choice! Yet, why do I feel like I should be ashamed of my actions?