The Sag Sun and Aries Sun are the "directors" of your personalities, and pull all the interpretation of the meanings of the other together. Since you are both Fire sign suns, you are both impulsive, passionate, and friendly. Being Aries, you change more and jump in and out of things more, the Sag is more serious, interested in education, or getting more involved in what the interests are. The Cancer and Libra Moons are called a square in astrology, and many people think they are "bad" and get scared of them. My love of 39 yrs. and I had both Moon and Venus squares. It adds challenge and chemistry, so the relationship doesn't get dull.
But you seem to be in a stagnant patch lately. I have different planets for each of you, so it's hard to compare. The Taurus Mercury one thinks in a stubborn way and doesn't change point of view easily. That can make for a boring time, we need to grow and change, to keep life interesting, and usually change our minds on some things as life goes on. Mercury in Sag is more of a deep thinker, and can also believe they are always right. So this can be the cause of communication issues. Taurus Mercury has to try to be a bit more open minded, but is sensible and sensual, probably can be coaxed out to do something new romantically. Mercury in Sag has to learn that they aren't always right, and can be open more to what the other one has to say. Your partner's Moon in Cancer means the feelings get easily hurt too, so tread lightly. If you've been together for 4 yrs., I think based on what you say here it is just a patch that will pass when you get interested in other things. Why not take a course together, or maybe try to go to some new places? Maybe you outgrew your friends, or just got bored. I think it's a good combo, talk about it and listen to each other, do something to get out of the rut. It happens in the best of relationships. Best of luck to you two! Jean