Marrying an illegal immigrant in Spain

Hello everyone! :)

I have a big problem that's been bothering me for a long time and I hope you guys can help me with an answer. I'm a Croatian girl, living in Croatia, and my boyfriend is Algerian who has been living in Spain for 6 years now (he overstayed his visa). He doesn't have documents and permissions to work there. We're both adults, over 21 years old.

So I wonder what could he do in this situation? Since I'm an EU citizen, could we marry in Spain in order for him to become legal? And how long would that process of him becoming legal last (how long would I need to be in Spain before we can both travel somewhere else)?

Thanks in advance!

Thanks! We are really in love and planning a future together, but obviously we have big obstacles in front of us, and it's making me nervous all the time. :/
So I really hope things go well... I'm planning to go in Spain next year so we could try to make it work.

If anyone else has some advice, I'd appreciate if you guys could share it with me.. thanks a lot! :)