to be fairly honest, you will distance away from alot of people in your lifetime
sometimes it just happens from one without a warning (like in your case) but if you were doing well enough to have a 'chemistry, connection' or however you describe it, with that one person, im pretty sure you'll find someone like that to get along with simillary.
also about feeling lonely, i mean who doesnt feel lonely, we will miss people, it will hit us hard at a point, i feel your pain, i guess obviously try to re-connect and find out why and what happened, but just don't be the only one putting all the effort in communicating back with eachother, because if he cared (hope he did) he would be happy to see you try and get back at you tbh, if not, then i guess you just have to eventually accept what has happened.
i hope i didn't come across rude, im just saying my opnion though x x