IMPORTANT I need advice Asap

So 2 to 3 weeks ago I was slept with my ex because it was sort of an ongoing thing. Then I met this new guy and things progressed really fast in these two weeks. Sleeping at his and seeing his family and stuff. Too fast. Then my ex asks if I want to stop sleeping with him cause he's getting that vibe and I say yeah I'm seeing someone and he wishes me the best. But we saw eachother yesterday and he said he wants everything to be open and confessed he wants to be with me which is what I've always wanted since we've broken up (3 months). I don't know what to do. I'm going to end up hurting one or the other. I don't know what to do. No hate please