Can I get any STDs from giving a handjob?

I'm 15 and wondering about ejaculation. my girlfriend's given me handjobs/blowjobs before but i've always stopped her before ejaculating. i just thought it was an extravagant porn type thing to come in her mouth, but the other day my friends convinced me otherwise. It's not because i'm too nervous, i just thought otherwise. is she expecting me to go in her mouth, or are most handjobs/blowjobs used for foreplay.

oh, and i'm partially asking this because (differently from when i masturbate) she gets me excited a lot quicker and it doesn't take long before I'm know im going to ejaculate. i've only got oral a few times, is it because these times are my first, or do you think i won't grow out of that.