wow, kinda weird, but be happy with what you have accomplished & set your own goals. if you have that stuff in future, fine, if not as long as you're happy & you realize things in life isn't always about materialistic things.
if you are scared why have you waited 5 years...obviously you love him & he loves you.
are you having urges or thoughts on your part & thinking he's having the same?
IF SHE CAN CHEAT THAT EASILY, SHE'LL DO IT AGAIN!!!
She only 19, MATURITY hasn't hit her yet about future and all that...you'll be back her in less than 6 months crying again that you found out she did it again!
TALK TO HER...don't yell or argue...if she startes yelling & can't TALK normailly then treat her like a w.hore and kick her to the curb...maybe then she'll realize she's in lala land or realize she's happier without you.
either way you'll get better soon since right now i'm sure its killing you knowing all this stuff is happening in the house where you also live.
no matter how good a date is, a guy will always remember if he slept with you within the first couple dates. men are stupid like that since they realized they got what they needed with no challenge. next time even though it feels awesome never sleep on the 1st or 2nd date, seriously.