Thinking of my college days, I always strongly disliked being an extra when a dating couple went on an outing. I rarely ended up as a third wheel because I simply wouldn't go if it looked like only one couple or only dating couples were going and I didn't have a date. I would rather spend the afternoon or evening alone.
When dating my MEM I felt the same way whenever we were with his mother. She had his complete and undivided attention. When going anywhere in the car, she would get the front seat as if that was the most natural thing in the world, I was hardly acknowledged. Even after we were married, I sat in the back and she claimed the front seat. At the table she would sit next to him and I would be on the other side of the table, as far as possible away from them.
Shortly after we married we went to his great aunts for Christmas, which was a 9 hour drive, but that was where his mother would be so we needed to be close. The entire stay I was hardly talked to, only by the great aunt who seemed oblivious to her niece ignoring me as much as possible. This went on every Holiday, ever weekend we had to go see my MEMs mother, every conversation they had he would take the phone to a different room and have a private conversation I was never part of, every get-together his family would have, I was the outsider, following along with the mother and my husband and it was a given that he would take care of his mother. Everybody pushed him into taking care of her, it was clear that that was his spot. His mother's caretaker.
We used to have a video made at our wedding. I cannot watch it. I must have thrown it away I haven't seen it for a long long time. Even at our wedding I was the third wheel. I didn't see the red flag, the big huge red flag, until long after I was married and completely depleted of energy, lonely, and unhappy. Married to a mem you are the third wheel, always and forever.
Here a picture to illustrate my wedding experience, one I do not like to remember.