Yes, being promiscuous can be bad for you. Not only is there the increased risk of STDs, there's also the increased risk of feeling like you have been used and feeling guilty for violating any moral precepts or whatever that you may (or may not) have concerning promiscuous sex. There is a website I have that I could recommend to you if you would like to see it.
But be forewarned, it is a religious site and I will not post it unless I will not be violating the rules and unless you request it. Not all of the reasons on this site for observing chastity are religious reasons but many of the reasons do have religious elements. But anyway, here are a couple of quotes from saints about chastity that you might find encouraging if you do choose to observe chastity:
"When you decide firmly to lead a clean life, Chastity will not be a burden on you: It will be a crown of triumph."
- Saint Josemaria Escriva
"Chastity is a difficult, long term matter; one must wait patiently for it to bear fruit, for the happiness of loving kindness which it must bring. But at the same time, chastity is the sure way to happiness."
- Pope John Paul II
"Purity prepares the soul for love, and love confirms the soul in purity."
- John Henry Cardinal Newman
I hope you do not mind me posting these saint quotes. If you do, let me know and I will gladly edit the post for you.