1) Neither party wants to keep it. However, under Thai law, they both have continuing obligations eg: paying fees or face criminal or civil/corporate liability.
Note: OP's question is for a recomentation to exit not continue by paying fees indefintiely - so your comment is irrelevant.
2) In contrast, previously I have provided options to exit; which, you have failed to do!
3) Again, under the laws of Thailand, there is no process of 'dissolution' (ie like in England & Wales via Companies House). Instead, the process requires "De-Registration" at the Thai Court.
We have assisted many clients with the process, and - unlike your comment - it can be both time consuming and expensive; particularly if 1 of the shareholders does not actively cooperate.
They are both shareholders in the Thai LLC. Therefore, until 1 or both of them are able to exit, they are stuck together - whether they like it or not.
If the Thai shareholder "walks-away" then s/he could face civil/corporate and/or criminal liability within Thailand.
The foreign shareholder could "walk-away" but, unless they exit the Kingdom and neither return or has any property/assets in the jurisdiction, could face similar consequences as the Thai shareholder.
Unfortunately, in this case, you do not have a practical solution.
If the companies remains registered, it shall incur annual accounting & regulatory fees.
You can try to sell it to a third-party for "basic" value to get-it-off-your-hands. However, presumably, the prospective seller shall conduct due diligence checks.
Otherwise, you shall require a Thai lawyer to institute De-Registration proceedings to close the company.
You could walk away and leave the liabilities for the main Thai shareholder. This may end your friendship; and, if you are in the Thai-jurisdiction, you could be involved in future corporate (and/or criminal for non-compliance with Thai DBD regulations) legal proceedings.
Due to the current Thai law regarding the non-recognition of same-gender marriages/civil partnerships, it is my understanding that you do not classify as a spouse or dependent.