1. Dissolve the group and sell the aircraft to a 3rd party.
or
2. Get an independent valuation, and one of you buy the other out completely. Obviously who ever both it would have the option of finding a new partner.
or
3. Base the aircraft 50% of the time close to him and 50% close to you.
or
4. Find a new airfield to base the aircraft on that's 50 miles from both of you.
It's not unreasonable for him to want decent access to the aircraft...after all he paid for 50% of the capital, and continues to pay 50% of the running costs.
What you both have to accept is that if you were living 100 miles apart from one another when you first thought of buying something together, you'd probably have dismissed the idea as unworkable fairly quickly, or would have had to make one of the above compromises.
Things change, and people move one. While it's true to say that it is him that has moved on, it's also unreasonable of you to expect him to leave the aircraft which he owns 50% of the capital in, right beside you, where he has little or no access to it, and to continue to pay 50% of the bills.
Baseing it 2 weeks beside him and 2 weeks beside you doesn't seem all that unreasonable to me under the circumstances. It's certainly more reasonable in my view than you insisting it stays beside you all the time.
dp