Will Sims 3 get wrecked if I try Sims 4 - since it's for free for a couple of days?

I don't feel like I'm done with the Sims 3, I'm still learning things about that amazing game.

I admit I've been broke since Sims 4 came out and have a very low entertainment budget, so I never really considered Sims 4.

I've asked a few people I know who've played both what they like better, I see most say they liked 3 better, but feel like they are stuck with 4.

So, if I download for free, and fire it up, what is going to happen to my Sims 3 game, can I go back to it?

Has anyone tried?

Thanks a lot,

Nancy