You're in love! Or maybe you just really like the person you're with! I'm so happy for you and really pleased that you seem to have found someone so awesome. You should be proud to hold hands and give occasional pecks on the cheek.
But do NOT, by ANY means think that it's okay to GIVE YOUR BOYFRIEND A BLOWJOB/FINGERBANG YOUR GIRLFRIEND ON THE SUBWAY. What, seriously?! I mean, making out in public is bad enough; no one likes huge amounts of PDA, especially if you're over the age of 17. But to totally have full-on sexual contact like that on a subway is absolutely gross. It's also really hard to NOT watch it (though if you're doing that you obviously enjoy voyeurism to a certain degree so I should be allowed to watch you).
Hey people that have almost-sex on the subway! YOU'RE ALL BIG JERKS!