Which way the 109 dives is also important. E management is key. More turn, higher G's = more E used. Smaller turn, lower G's = less E used. It looks like the 109 is crossing close to 90 degrees left to right in front of the spit. So diving below the spit and pulling towards his tail would pull a turn close to or less than 90 degrees from his current flight path, and he can pull very few G's doing it. The spit (if he wants to keep on the 109s tail) has to roll his plane (since an immelman is impossible at these speeds) and pull a full 180... possibly even at 7-9 G turn.
109 - shallower turn, less G's = less E used
Spit - tighter turn, higher G's = more E used.
I also think the 109E is a better diver than a Spit 1 (not sure though), so he'll get a bit more E with that advantage as well. Yes, diving does use up alt and if you're put onto the deck then you lose half of your options, but in this situation it looks like the best option for him that I can see. If he continues straight then the spit will turn onto his six. If he tries to roll over and climb then the spit will get him before he can even roll over. If he tries to roll away from the spit as if trying to line up an overshoot shot then he gives the spit his 6. Not sure of the separation between them here, but if they're both near a stall then the spit would have to be wicked close to force an overshoot this way.
Getting into a turn fight with a Spit 1 in your Emil is not un-winnable, but it will be very difficult. This 109 has obviously made a mistake and is in a very very bad spot. Diving for speed and separation, disengaging, and then re-positioning from a better position looks like his best option IMO. Just my thoughts. Might not be the right one, most definitely not the only option available either.