First time buying condoms🙈🙊

Hi! Well Ummmm how to start?

So I been dating this guy for a while, he lives far away and we are both new to the having sex thing, well in all honestly I have had sex with women(strap ons a few times) but never with men, and he is a full on virgin, not even a first kiss.... and we are planning on doing it soon when we see each other but.... neither of us is very experienced in the matter of condoms.... I know how to put them on but I do NOT know what size I should buy for him... so I need some advice!

(We are both in our early 20s) Pleaseee dont judge 😳