Most women cheat on their man for one reason and one reason only - you are not getting the job down in the sack. If you were she wouldnt feel the need to seek it elsewhere.
Words of advice. If you're a 2 pump chump that cant go long enough to get your girl off, start beating off more. You're sensitivity level will go down, you'll last longer, she'll get off, and you will too eventually, everyone's happy. If you suspect you'll have sex that nite, rub one out 4-5 hours before you see her.
If you're one of those cats who cant get it up, STOP jerking off so much, your sensitivity level will go UP, making it easier to get hard. Now you may have to work hard not to blow your shizzle too quick, but she'll be pleased you at least were aroused enough by her to get it up and in.
You have to find a balance. If you want to keep your woman happy, truly happy - go downtown often, and dont expect her to return the favor. If you do this, she will worship you. Very few guys care enough about their girl to just satisfy them and not get the payoff afterwards...
If you cant find the common ground, get yourself some Levitra and pop those suckers like candy on gameday. If you care enough about your woman, you will do whatever it takes it keep that beeyotch in your bed, and your bed only.