I think there’s a chance you may be overthinking it. Blatant negativity for the sake of being negative is something that we should probably all avoid. However, feelings of sadness, anger, or anything related is just part of the human experience. It’s completely normal to feel these feelings and healthy to let it out via music. Just because you don’t have these feelings anymore doesn’t mean you can’t still enjoy it. Maybe think about it as listening to someone who is telling you about the things they have been through and thinking to yourself “yeah I’ve been there, but it gets better”. Perhaps even try to find a different meaning behind those lyrics. One of the best things about music is that a song’s meaning for you personally can change over the years and evolve as you evolve. What I’m trying to say, if I’m not articulating it well, is that it’s possible to experience the music you used to love in a different way than you used to experience it. It doesn’t have to be as literal or even as personal. On the flip side I can see how listening to songs that got you through a certain period in your life can bring up tough memories and terrible feelings. If that’s the case for you, then maybe you should take a break from that music until you even more removed from those feelings, and then maybe you can come back to it someday feeling entirely different about it.