Want to marry to avoid loneliness

I am a 47-year old single woman and have been in a relationship with a man for over ten years now. We decided not to marry because we didn’t believe in the institution and didn’t want unnecessary complications. We also like our arrangement. We are both financially independent and live in separate apartments because we also like our space. I have been thinking about getting married to him though, because as I get older, I am starting to worry about companionship in my later years. I know this is selfish of me, but I don’t know what I will do if he decides to leave me. I can’t even think about dating again in the future. Is this a sensible decision or am I just being paranoid?
You are not being paranoid and are entitled to change your mind about your arrangement any time you like because you alone know how you feel about the need for companionship. There are pros and cons to every arrangement, of course, but you and your partner alone are capable of working this out and arriving at a solution that works. Marriage is no guarantee of someone staying in a relationship, and it makes more sense to focus on the strength and stability of what you both have. Speak to him about your fears and ask him what he thinks can be done to address them. 

How do I tell my boyfriend that I don’t like his friends without hurting his feelings?
You can be diplomatic or be open and honest if you reach a point where you can’t pretend anymore. Either way, a healthy relationship is one where both partners feel safe to talk about anything, even topics that seem difficult or awkward to handle. If you don’t like his friends, give him your reasons and tell him why you aren’t comfortable meeting them. You can always arrive at a compromise that works.