I don't own a horse. But I do know, from knowing lots of folks who do own them, that there is always soooo much more to owning, and to the horse themself than you would at first assume.
Riding that horse for three weeks and out on 4 trail rides is nothing more than the tiniest Peek into his personality. Are you able to do some other things with him, such as arena ride, you may get a better feel for whether he is right for you. Do you feed him? groom and tack him? I don't know the situation at your lease.
There are plenty of sales where the buyer has no more than a couple of hours with the horse before making the decision, so you've got more than that. But if you, yourself , are nto an experienced horseperson, then please have a trainer (not the seller's trainer) look over the horse and maybe ride him. And a vet check is always advisable.
IN any case, not to rain on your parade. It is cool that you are ready to make that big committment. bravo!