I broke my best friend's trust and really want to make things right

Assalamu alaikum, everyone. I’m dealing with a tough situation and could use some advice. I’ve been close friends with this brother for years now-he’s like family to me. Things got really complicated when I developed feelings for his sister. I know the right thing would’ve been to talk to him first, get his permission, and handle it properly. But I got scared it might upset him, so I kept it quiet and ended up talking to her instead. I confessed my feelings, but she wasn’t interested, and we stopped talking. Later, she told him everything. We had a long, honest talk where he said I broke his trust by hiding things and making immature choices. Alhamdulillah, he’s forgiving and kind-he said he forgives me, but it’s hard to forget. This friendship means so much to me, and I’m determined to rebuild that trust. How can I show him I truly regret what I did and prove I’m a trustworthy friend again?