The reality is that it depends on the terms of your agreement. And the problem is that you did not get an agreement in writing at the start of this that specified exactly how this venture was going to work. There were all kinds of ways that this could be structured. It is possible, for example to have an arrangement where the split of capital and the split of profits are not the same (though that is not the most common way such investments are done). I don’t know the details of what you and your partner would say was the deal you made. It may be that you didn't really discuss it much. It may also be that you each have different recollections of what the agreement was.

It is not unusual for the percentage ownership in a venture to be based on the relative amounts of money and property that were contributed to the venture. You contributed $12,000 and he contributed $5,500 for a total contribution of $17,500. So if the ownership was split based on contributions, he would have 31.43% of it and you would have 68.57% of it. You might argue that you should have even more of the venture since you did most of the work in running it. The problem is, though, that you have been splitting the income 50% each and my guess is that you reported on the tax returns that he owned 50% of both the income and the capital. That is evidence that he can use to support a claim that he owns 50% of the venture.

What a court would decide is impossible to guess. It would matter what each of you testified as to what the deal was and what evidence you each presented to support what the deal was, which might include more than just what was contributed and what the profit split was. The fact that you are getting different answers from different attorneys tells you that there is no clear cut answer to give you and the result in court is simply not going to be easily predictable. That's the problem you run into when you don't get a well drafted partnership agreement that spells everything out in detail. Even when your partners are family, friends, or lovers you need to treat business ventures with them like you would with a stranger and get everything in writing and then make sure everyone sticks to that agreement. So should you ever go into business with anyone else in the future, keep that in mind and don't repeat that mistake.

There is also the issue of figuring out exactly what the LLC is worth.

If you can, negotiate a deal on the split with your ex-partner. You might try offering him, say, 30% of the value of the LLC (or whatever you think his share is) and see if he’ll take it. If you say you can have a check for that ready immediately, the lure of getting the money right now might get him to take it. If he won't take it, then you get into the back and forth of negotiating and hopefully you can arrive at an agreement. If you do, make sure you get a signed agreement from him that the payment is in full satisfaction of his interests in the investment and that he waives any future claim to anything from the business. See a business attorney to get that drafted, and make sure he signs it at the same time you give him the check.