This sounds like grief and depression to me. You're struggling because you're still mentally filtering everything you do through another person who is no longer part of your life. You must learn to do things for you, not for someone else. You may find that some things you thought you enjoyed you actually were only doing for someone else. Likewise, you may discover that what you want do purely for yourself is different from what you might expect or predict.

Time will heal some of this naturally. But the #1 recommendation I would always make to anyone in this situation is to pursue exercise. Weightlifting, hiking, etc., generate rapidly compounding results across multiple dimensions of your life and also often generate some of the most authentic social experiences you can find as a 30+ year old adult.