I'm Struggling to Feel Remorse for My Mistakes

Assalamu alaikum. It's hard to open up about this, but I really need some advice. I've been struggling with a certain bad habit for a long time, since I was really young. Even though I wasn't raised with the deen at first, Alhamdulillah, I found Islam later. I know these actions pull me away from Allah's path. Even during this blessed month of Ramadan, it hasn't been easy. After falling into this sin, I often feel too drained and lazy to pray Fajr and Dhuhr on time because I need to make ghusl first. I end up wasting time in bed until I finally get myself together. The scary part is I don't feel the guilt I should feel anymore. Sometimes, right before I do it, I remember that Allah is watching, but I go ahead anyway. Last year, I managed to stop for nine months straight, SubhanAllah, but then I broke the streak and I don't even know why. For some perspective, I quit vaping two years ago, Alhamdulillah. Now, I'm about to turn 19, and sometimes I think about marriage just to have a halal outlet and finally stop this for good, not even really for love, which feels selfish. I feel like constantly doing this sin and missing prayers is making my heart harder, and that's why the guilt is fading. Wallahi, I've tried everything to stop. I just don't know what else to do.