It's not possible for me to be emotionally invested in anything because I'm profoundly disappointed in life. I want a refund.
When nothing works, go for delusions (only if you're stable enough to not have them break apart the nature of your reality too much).
Also, go travel; be it on the other side of the city in a new coffee shop, in a new town for their town's day or sth, or in a new state/country/continent, travel somehow manages to shuffle the internals in one's brain enough to reboot to a different baseline; good trick for when current internal state is too meah.
Those are some heuristics I'm using for dealing with my own inner despair when it comes and they have only a sparse intersection with proper dealings of depression.
For example, we visit our local hospital every weekend to hand out magazines, books, and toys to people whose lives have been affected by an accident or illness. It's rewarding, and the group of volunteers changes each month, so you get to help others and meet new people. Helping others is also a great way to help yourself. Afterwards, we usually spend an hour or two socialising at a bar near the hospital. The doctors know us, and they sometimes join our table.
If that doesn't work either, exercise and therapy have worked for some of my friends. Having a personal trainer two or three times a week is often better than going to the gym on your own, and seeing a life coach or therapist once a week can really help you move forward.