Well, technically, with the comics code in the past and all, this has been open to much debate.
Some people reckon he would've slept with Betty Brant bak in the 60's, some reckon that they were only 1st base teenagers. We'll never know for sure, as not much was allowed in comics in those days. Believe it or not, Stan Lee really pushed many boundaries and managed in the best way he could, to get around this stuff and not be shut down
Now, for most people Gwen was Pete's 1st. Stan Lee even called them lovers back in the swinging 60's. He even refered to Pete as a 'swinger.' Lol
This is one of the many things that pissed off a lot of people in the Sins Past arc, JMS tried to retcon it. This REALLY pissed me off. Stan Lee's run of Pete's college days, and Loeb's Spider-Man:Blue, (which is both inspired and set in the college days,) are both considered some of the best Spidey stories ever told. Stan heavily implied as much as he could, that they did, do the nasty. LIke I said, he even called them lovers. Don't forget, at this time Stan was working very hard to keep his older college audience, and have it grow larger. A more mature Peter, dealing with serious issues on college campus,' drugs, death, and mature relationship problems fit in with this ideal. Don't forget, at this time Stan was touring the colleges of America giving lectures on the world he created. When Jeph did his story, he followed this suit, and touchingly showed the scene where Pete and Gwen took the 1st steps to an, 'intimate,' relationship. This is the main thought of Peters 1st
We also had The Black Cat. This was during the 'grim and gritty,' 80's mainly, so it was expected that they had a full on relationship. And with a girl like her, it sure would be hard not to! Besides, there's no way in hell a girl like Felicia would stay in a PG relationship while living so tightly with someone! Lol
Obviously MJ too, apparently, was it, ASM 158 was their supposed 1st time? I have no idea their 1st time. Although, according to PAD, this was Pete's 1st. Most people think that's BS though. I know I do
Sorry if I forgot anything relevant, but that's it I thinks!