I started lifting for girls, but after I started seeing gains, I switched to lifting for myself and beating my own PRs to be able to be strong physically.
There's a lot of activities I want to do, that need a good strong body and endurance to be able to enjoy it to its fullest. Scuba & salsa/mamba/swing dancing are my future goals. The rest comes from incremental gains you make socially.
I signed up for an electronic music meetup, there was a 5k event, I went there; I had a choice (when I was getting my shirt to get a tee or a tank), I took the risk and got the tank and I owned it. I wore that confidence, I smiled and had a good time. Met a girl along the way, got her number; got a dinner date with her on Wed. Regardless of what happens with her, I'll keep lifting because I have goals that drive those lifts. Its a positive reinforcing loop, a self-fulfilling prophecy.
The way I see now, is that if you have goals and you work hard towards those goals, are willing to take even the smallest of steps forward and don't hesitate in those decisions; things will work out. Girls like guys like that. To them its "oh he's passionate and dedicated, he plans ahead and follows through--he does interesting things with social value. He likes to explore, he's got culture, etc."
All those experiences add up for you, they give you things to talk about, things you saw, heard, learned about--things you can share with someone else. They're stories. Girls LOVE stories. Stories, experiences that are attainable = value. They'll want to be with you, if not for a relationship, if not for sex, then at least as a friend to be able to experience the things you have. And during all this, you just gotta take those baby steps forward, close the physical distance, occasionally touch, sometimes slip the arm around the waist, etc.
Eventually, that leads to sex or more fulfilling long-term--and if nothing else, more pics for your social prof that you're not a loner/loser. More Value.