i envy people who are in relationships

i find it hard not to, because i am a male in my middle age, who has never had a relationship because i had mental problems my entire adult life, and i missed out massively...i did have flings with girls in my teenage years but no steady girlfriend....so when i see people in relationships now, or just see guys interacting with girls and getting somewhere, i feel envious, jealous almost...because i never had that...and still haven't got it.

no, i live in a flat by myself, with just my elderly parents for support now, and i soldier on alone....how is that fair?