To expand on my 'one night stand' theory:
"Lie awake completely satisfied and let the sweat run through my hair" - It's just after having sex; the euphoric satisfaction.
"Well, I haven't felt this way in quite some time" - Maybe he hasn't had sex for a long time or sex this good
"when I look over your not there" - he looks across the bed but she's not there
"rain on my parade" - ruin my happiness
"That you won't ever really be mine" - although he really wants her more than just a one night stand, he realises that she doesn't and he accepts it.
To expand on my 'one night stand' theory: "Lie awake completely satisfied and let the sweat run through my hair" - It's just after having sex; the euphoric satisfaction. "Well, I haven't felt this way in quite some time" - Maybe he hasn't had sex for a long time or sex this good "when I look over your not there" - he looks across the bed but she's not there "rain on my parade" - ruin my happiness "That you won't ever really be mine" - although he really wants her more than just a one night stand, he realises that she doesn't and he accepts it.