Offer but no offer!?🤕

I had an interview yesterday from a safe school, but the research group is very good. The PI was extremely impressed with my CV and loves to have me in their group. But he said that he would process an offer letter if I decided to join their group. The problem is, I haven't heard back from any of the other universities which I have applied to. I told this PI that I'll have a decision near the end of Feb. But I'm worried about losing this opportunity as well as the others and end up with nothing. Should I confirm to join here and wait with an offer letter or should I wait as it is? It's a weird situation; pls share your insights🥲