I have holidayed on my own several times since my husband died, the thing to do is to act as though there is somebody with you who is just not up to a boat trip, market outing, or a long walk along the prom. The other thing is to have a good book, kindle or newspaper you can pick up when you get fed up with the couple canoodling beside you, or the family group sharing their sandwiches. My friend does not swim or like being in direct sunshine, so on our last trip together she stayed at one end of the boat, while I joined the swimming crowd at the other. Nobody knew who was with who anyway. Its only a problem if you let it be.