I live alone. I have a dog most of the time, but for right now she is staying with my parents. I got in trouble for having her (not supposed to be in my apartment).
I don't have any partner or whatever. What do I do when I get lonely? Watch TV, talk with friends, go over to some friends house, go to a party, hang out at work (rock climbing gym), take a nap, or whatever. I spend enough time with people that I don't think I get too lonely. What about lonely, like when I feel like a partner would be nice? I watch a love story from my collection, take run on my treadmill, talk to my friends about it, or go to a party.
What do I do about sex? Nothing. I'm not getting any right now, and I don't want any right now (although that seems to change when I party and get a little drunk and frisky...).
I guess it depends on a lot of things. I'm in college, so it's easy for me to not be lonely, or whatever, and if I really want to get some sex, it wouldn't be that hard. I know this isn't everyone's situation, but it's mine.
Hope it helps.