Center object ie. a circle between 2 other objects ie. 2 lines

I am currently designing a set of vambraces, and am trying to place the lace holes between the outer cut line and in inner design groove line. the two lines are angled and are .5 in. apart, I would like like to place the .125 in. circle directly in the center of these two lines. It would be wonderful if I could place it at an exact distance from a third line that is above it too.

If I could figure out how to place the center point at an exact difference away from those 3 lines without figuring out the exact x,y coordinates it would make my life much easier.

Thank you in advance

It's a bit tough to follow your explanations, not sure if I understood correct.

But basically, even in CAD I mostly use techniques I'd use on paper too.
E.g. drawing construction lines, parallel or orthogonal lines or circles to find intersections needed for the drawing.
These lines can be placed on a separate layer to switched off or be deleted when no longer needed.

It's a bit easier in CAD as you can use snap tools to catch line endings, centers or the middle of a line.

For reference see https://docs.librecad.org/en/latest/ref/snaps.html#snapping

If I understand correct, you have 2 nonparalel lines and want to draw a circle centered between them.

What I would do is to draw an auxiliary line centered to them, for example, draw two tangential circles "Tangential 2 circles 1 point" appart enough as their centers guide your auxiliary line. Any circle you draw with center in the auxiliary line will be centered between your nonparalel lines.

If in plus you want the circle be at a known distance from a 3rd line, then draw another auxiliary line parallel to that 3rd line and center the circle at the intersection between the 2 auxiliary lines.

If instead you want the circle be equally separated from the 3 lines, then it is easier:
Draw a tangential circle to the 3 lines "Tangential 3 circles" and draw the final circle  centered in the tangential one.

HTH
Pere