Does your partner care about you or not? and if this means they don't care about their partner why do they stay together?

I notice that in a lot of relationships especially the one i was in i would care about my partner his well being. So When his or her partner sees that they drink a lot or have an unhealthy habit and do that bad habit pretty often and their partner never talks about it with their partner see what's going on whats wrong etc and just let him or her be. Or hangout with friends that like to party a lot and their partner gets invited pretty often and he or she goes, but the partner never has a talk about this with her or him.
Does your partner care about you or not? and if this means they don't care about their partner why do they stay together?
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