AITAH overreacting to my roommate refusing to pay a bill until later?

So my roommate and I who have been friends since second grade moved in together for college last month. This is our second month of bills and last month was no problem. Every bill is in my name (because I am more responsible) and today our electricity bill came in. Tonight I paid it, I went to his room and let him know that I paid and gave him the total of his half and said please Venmo me. He said that I would have to wait because he wants to use his the GI bill to pay for it. This upset me because my money has already been taken out of my account and I am waiting on his half then. I told him I would appreciate it if he paid me now instead and he refused and told me that I will have to wait and that he never agreed with me that his half had to be paid immediately. He then proceeded to say that basically I am going to have to deal with it since I’m the one that wanted control of the bills.

I proceeded to go out to my car and call and ask my parents their advice and they said that I should set a specific day for him to pay me and that there won’t be any question. We agreed to three days before the first of each month (this would be the amount of time for his Venmo to transfer into my bank account) I went back inside and told him that this is what we came up with and he flat out refused again.

He stated that he does not want to take any money out of his savings account (I know he has money in it because he’s told me the amount before.) I told him that I do not have the benefit of receiving a check to cover my bills and mine is all coming out of pocket unlike his. My parents are going to talk to his dad about this but I feel guilty and don’t want to cause tension or stress between us.