That is an excellent question, and it has to do with who they are and their connection to Hashem. It also has to do with the people around them and whether they treat them as equals or they are condensending. Being single is a difficult nisayon but it doesn’t take away from an individual’s personality, intelligence, humor, ability to love, be a good friend, etc.
Friends, neighbors and family should include singles just as one would include others. It is up to the individual to accept or declne an invitation. Just because a person happens to be single that doesn’t mean that their life stops to exist. When they are still part and parcel of everyone’s everyday life they are less likely to lose their moral code. IMHO, it is when they are left alone and feel rejected in all areas of their lives that they feel alone and outcast that they feel that Hashem has abandoned them and that is when they let their guards down and give up or give in. That is also when they choose to move to a community of singles and that is the worst scenario possible. When that happens they become friends but forget to consider each other as possible prospects. The friend concept takes them out of the running for possible spouses for some reason although an outsider will point out that they can easily become mates. Amongst the single crowd they can only see each other as “friends”.