How to connect 2 meshes without messing up the textures? So, when I try to combine 2 different meshes by adding a Boolean modifier and then filling in the gaps by selecting vertices and pressing F, the textures get really messed up. There are a bunch of lines that cut through the rest of the texture that connect the 2 merged objects. How do I prevent this? I am using the old version of blender, by the way.
By "old version" I assume you mean 2.79?

What you're looking for is a UV seam. This will prevent the connecting mesh from insisting on bridging between your two original shapes directly, and allow you to position it individually.

For 2.79, select the edge between your connection and your original shape; then hit CTRL+E. You should have the option "Mark Seam" available. This should disconnect the UV map along the corresponding edge, so you can move its vertices independently of the others.

For further details, consider reading the documentation on it for 2.79.