Triads are complex and hard. There will be more bumps in the road like this. Things that are harder than expected for her, for you, for him. It can be hard to predict, and there may well be deal breakers down the road. Being in constant, close proximity will make everything 50x harder. I would strongly suggest waiting until the relationship is at least at the 1 year mark before considering everyone living together.
That said, did you do something wrong? Yes and no, that's a very subjective question. I don't think it's objectively "wrong" to say "threesomes only" but I do think it'd inaccurate to have that rule in effect and consider what you're doing to be a real, serious relationship of the depth to be ready to consider blending your lives. I'm a huge fan of threesomes, but I believe that one-on-one time is crucial for building real intimacy.
Some reading that may help:
Best of luck!
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.