I imagine that you, being an older sister, have always taken care of your younger brother (and any other younger siblings you may have). It is natural for older siblings to take on the role of surrogate parents.
But even parents, at some point, must let go of their children and allow them to lead a life that the children choose – for better or worse – for themselves. From what you’ve shared, it seems that your brother is quite content in the life that he is presently leading. He has a wonderful network of family and friends, and “he’s not lonely.”
If your brother has not openly complained about giving up on love, perhaps he is simply enjoying his social network and is taking a break from romantic relations. Perhaps “finding that special someone” is not a priority for him right now. Isn’t this okay? Shouldn’t we respect his decision?
When we try to help someone who doesn’t ask for help, we make the situation more about ourselves than the person we are trying to supposedly help. My therapist antennae are sensing that this is what’s going on here. Ask yourself why it’s so important for you to see your brother coupled up with a romantic partner. Do you believe he will be happier? Ask yourself what fears you have of your brother not finding that special someone. Will he be sad?
Whether your brother is or is not with someone, or whether he is happy or sad, is his responsibility – not yours. Do not make this about you and what you consider is best for your brother. Let’s say, hypothetically speaking, that your brother starts dating someone and they are having conflicts. I presume that you will “worry” and want to “help him.” Let’s continue and say that your brother gets dumped by this ‘partner,’ you will worry and want to help him. It’s wonderful to be concerned about a loved one and help this person when he/she asks for help. When you try to help your brother by imposing your values (i.e., he should find someone special) on him, you’re not helping him; in reality, you’re stripping him of the control that he needs in his life.
If you really want to help your brother, please accept the fact that he is forty years old, and he has the right to live his life in the manner he chooses to live it.