Series A investors typically want 30% to 35% of your company. If you have already given 50% to an accelerator, there is no room left for another investor.
You and your co-founder will loose motivation to work for the company. Let's say you give 50% to the investor, create a 20% options pool, and split rest of the 30% with your co-founder. Fast forward 1 year where you have 15% equity, your company is out of cash and unable to obtain next round of funding, and you are sleeping under your desk to run the company. You will have no motivation to continue working for the 15% equity you have, and will eventually give up.