I may be cripplingly old fashioned, but I do think there's something wrong with that many casual partners on that time frame - I'm a sex in relationships kind of guy - and when I break that I generally feel crap for months (However I'm 22 and have had 3 sexual partners - enforced by me, generally (ironically, 2 were 'casual' in the sense that there was no formal relationship ('taking it easy and simple' they said), but they lasted a few months and were solely with the same people).

It's normal for you to be jealous in this case, and I definitely don't think you should be happy that he enjoyed himself in that way! :P

Are your objections of his lifestyle because of your moral code, or just because it makes you feel unimportant/unloved? Or is it because it makes you feel like you're not taking advantage of life?

Don't beat yourself up so much about it - you're definitely not alone (and I don't think that normal human beings enjoy having sex with random people either - but again, I'm an unconventional conservative).

Try to resist punching him in the face.