<human>: Whenever we hang out, I'm pretty much perfect when it comes to attractiveness. I say the right things, do the right things, have her laughing and aroused. However, my problem has always been that I can't keep that up so by the time we have any privacy, all the sexual tension is gone and she becomes uninterested in sex.

For example, the other night, we went out to a bar and drank and danced and just had a great time together. She then gets very sexual and physical with me there with the kissing, and touching and rubbing and so forth. We decided to continue this back at her place. However, in that 25-30 mins it took on the subway to get back home, I don't know what I did but she lost that arousal completely and when we arrived we just kissed a little, cuddled and went to bed. 

I do admit that my mindset is totally different once I'm on the way back. I don't know why. When I was on the subway, I couldn't stop thinking about where and how I'm gonna bang her. Maybe we start talking about other things while we're sitting down so all the tension just evaporates? Sometimes there are moments of silence between us so that could be it too?

How can I keep up the momentum on the way there? When we just have sex, I usually do a good job of teasing her and building anticipation instead of just jumping right in. However, I just can't seem to do that when I'm outside.

I know I can't force her to have sex with me or complain and throw a tantrum--that'd just ruin the mood completely and would probably turn her off from sex even more. Sometimes I'd get bold and finger her while on the ride back but 90% of the time, there are usually a lot of people on the train. 

What kind of things can I do or say or how should I behave with her during that crucial point? How can I keep her aroused and in anticipation so that she can't wait until we start fucking?

We're both 23 year olds.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: I get my GF hot and bothered but on the ride home, she just loses the arousal so we end up sleeping instead of sex. How do I keep the tension and close the deal?