I agree that gym can be a hobby, but I think that it only becomes that when you live a lifestyle based around fitness. Like, you're doing lots of fitness related shit, and that is your hobby.
If you just lift 3 times a week and don't really do anything else, I don't think that's a hobby, or not really at least.
I agree with the other posters though. Breakups suck man, that never really changes, but they're never the end of the world. Feelings change, you stop giving as much of a shit over time, you learn how to cope with them better.
If you just broke up recently, take some time to grieve, that's a normal thing to do. Feel shitty about yourself for a week or two, but you need to start to try to move on, and you can't do that as easily without actually having anything to do. You don't have any hobbies, so when you can't rely on your friends to distract you, you're just focusing on feeling shitty.
Do you have anything you'd been interested in doing? An instrument you thought was particularly cool and you'd wanted to learn? Hiking? Some sport (can be individual, shit like archery or target shooting are still sports)? I don't know really, I have no idea what you're into, but do you not have anything you'd wanted to do bar lifting and hanging out with friends?
And though there's a lot of people who get insulted for playing vidya, it's definitely a hobby that lets you meet people as well, as long as you do it in moderation and it's not the only thing you do. I've met some great longer term friends through games.
But yeah, that's really the only advice that anyone can give. It's alright to feel shitty for a while, especially around valentines, but you need to start to self actualise. Get out there, expand your horizons. Try new shit out, you don't have to stick with it, but if you thought something sounded interesting, try giving it a go. You're already way too reliant on other people to keep you entertained, to the point that as you said, you end up just sitting around doing nothing if people are busy, finding someone else who's got nothing else to do to rely on won't do you any good at all, you'll just end up in the same situation whenever they end up being too busy to talk.
Ignore the fucking retarded robot by the way, and if you're someone who browses 4chan much, stop doing that. It gives you a steadPost too long. Click here to view the full text.