Marathon Consideration

Ok, people, here's the deal. I've been running consistently since I moved here and in the last 2 years I have upped the ante, so to speak, and started training for longer distances. I completed my third half marathon in March and thought that's the furthest I will run. Well, I'm now considering a full marathon. The race is in March, so there is plenty of time to prep (both physically and mentally). Here is my concern: my mind always checks out around mile 10. I'm much more concerned for my mental health than my physical health. Nonetheless, my running partner has already registered. So, if I ever want to attempt a full, I should do it with someone. You can't run 20 miles alone...well, I can't run 20 miles alone. So, um, what do you think? Should I just go for it? I'm taking a poll prior to registering...