Aleister Crowley described the abilities of magick as "it is theoretically possible to cause in any object any change of which that object is capable by nature."
Magick is a science and it is limited by certain observable laws. Magick cannot do things which we already think of as impossible like fly or turn into wolves because neither of those are in the inherent nature of a human. We don't fly. We don't change shape. That's just part of being human.
Relationships can start, grow, and end all on their own, and so magick can also do these things. You can create physical barriers to keep physical things out (walls and fences), and so you can use magick to create magickal barriers to keep magickal things out (circle castings and banishings). People both get pregnant and can do things to help ensure fertility, and so magick can also help ensure fertility and aid pregnancy. People heal from illness and injury, and so magick can help cure illness and mend injuries.
Things get a little more complicated when we start addressing distinctly mystical things like invoking angels or demons, but in general magick can only do something which is possible without magick. It doesn't need to be likely or easy, just possible.