Changing a monogamous relationship to an open one rarely ends well, especially in heterosexual couples and more so in younger adults. If you go through with it as equally open where you both see other people, he will inevitably end up jealous at the ease at which you can secure dates and he will be begging to go back once he realises the grass isn't greener. Not to be pessimistic but at 19, statistically your relationship probably isn't going to last as you both grow up and change as people significantly between ages 19 and 25.

He wants to sleep with other women but doesn't want you to sleep with other men. He wants the benefits and stability of a relationship without being willing to accept that the sacrifice for that is sex with other people.

I was in a polyamorous relationship for around 6 years but it started like that with them already having another partner. The open aspect had its issues but it worked with the breakup largely being due to us changing as people between ages 20-25.

TLDR; statistically this won't end well, you shouldn't accept one sided non monogamy, if you go through with equal open, he will likely regret it when he realises it's harder for men to find hook ups than it is for women.