Am I Really Sincere in My Repentance If Thoughts Sometimes Linger?

Assalamu alaikum brothers and sisters, I've been doing a lot of thinking about repentance and sincerity lately and could use some advice. Before I became more serious about my faith, I was involved in a relationship that crossed boundaries. I deeply regret that now and have sought Allah's forgiveness many times. Since then, I've worked to change my behavior, focus on my deen, and build a future that aligns with Islamic values. Alhamdulillah, I feel I'm in a much better place spiritually now than I was a few years ago. But I keep wondering - is my repentance truly sincere? Even though I regret what happened and don't want to return to that lifestyle, sometimes memories pop up and part of me still feels drawn to those experiences. I don't act on these thoughts, but their very existence makes me question myself. There's one specific thing that bothers me too. At one point in that relationship, we stopped short of going further with something I really wanted. Even though it didn't happen, I sometimes think about it. Part of me hopes that one day, if Allah blesses me with marriage, I might experience that kind of intimacy with my wife in a halal way. But then I worry - what if my future wife isn't comfortable with it, or believes it isn't permissible? In those moments, I sometimes hear whispers saying I had my chance years ago and didn't take it, and maybe I'll never get to experience it now. I know these thoughts are probably from Shaytaan, but they still make me wonder if I'd be able to resist such temptations. Another thought that troubles me is that maybe it's easier for me to repent now simply because I'm no longer in that environment where temptation was so accessible. If I were in that situation again, would I stay strong? I really want to believe I would, but the uncertainty makes me question whether my repentance is truly sincere. I genuinely want to move forward, leave my past behind, and build a halal future. I ask Allah often for forgiveness and guidance. But I struggle with doubt about whether my repentance is pure enough when these memories or desires sometimes resurface. Is it normal for someone who has repented to still experience these kinds of thoughts? How do you deal with doubts about whether your repentance is sincere? How will I know when Allah has forgiven me for the sins I regret so deeply? Jazakum Allahu khayran for any advice you can share.