I myself am gay, most definitely don't like being single, experience loneliness and also sadness. As for trust, well it is slightly hard for me, but not because of bad relationship experiences, something else. I don't know if I can help, I'll do my best. I would suggest you try to join groups in your area that are based around interests of yours (e.g. running or book reading). This may help you connect with like-minded individuals and thus hopefully reduce your loneliness and sadness. They may also be gay groups you could join. On the other hand you could also try to be more open (I don't know if you are) about your sexuality and approach people (even those you're interested in, regarding potential partners) as friends (hope for something more than friendship, but just enjoy the experience regardless of what may or may not happen). Other people have suggested to me to get a pet, or plants to help with loneliness. I think regarding the gay aspect try not to focus to much of having a relationship (but be open to it), instead, as mentioned, approach life/activities naturally, openly and doing activities you enjoy (and enjoy it). Perhaps also try be guarded at first with people and as you get to know someone (and see them as trustworthy) open up more to them, as appropriate.

Really hope I've helped, if not, best of luck with everything nonetheless. Feel free to private message me if you'd like