My understanding of hydraulics is limited at best but this is how mine is set up: The high pressure line was cut (just like yours). The side coming off the pump runs into the pressure inlet port on the valve. The second hose runs out of the power beyond port of the valve and connects to the other side of the pressure line that was cut (thus continuing the fully pressurized fluid from the pump to function the 3 point hitch). The 3rd port on the valve is the tank port and a hose runs from it and dumps fluid back into the hydraulic reservoir(transmission case). With just the two lines that you have, I can see how the loader would work and since pressure is ( I guess) being returned to your hydraulic line on the tractor, your 3 point hitch would work with this set up. What I don't understand (and think is probably vital) is that your present method does not allow for fluid to exhaust back to the reservoir. i.e., when you extend a cylinder on the loader the cylinder is full of fluid from being retracted- (since the cylinder uses hydraulic pressure to push the rod in or out of the cylinder, the cylinders are always full of oil). When you cycle the cylinder either in or out the oil that is being pushed out of the cylinder needs someplace to go and that is where the return to tank (reservoir) comes in. With only two hoses it seems the exhausted fluid is either returning to the second side of the high pressure line running to your 3 point (which would compromise its ability to work correctly) or being pressurized within the loader system itself and with no relief would probably damage something in quick order.
As I said, I am just beginning to understand the basics but it seems to me that with this current set up, you are either going to damage the system or have a 3 point that will not work properly when a load is put on it.
Don't know if this helped or not. Probably the best thing to do if you have more questions would be to pose your question on the "hydraulics" forum to elicit a response from those on the site that have a comprehensive understanding of what you need.