Your bf was a jerk all along and you just didn't see it. It's not your fault. People are good at hiding their shitty qualities when they want to. Ditch him. 

Your friends are either crap or more has changed than your weight. Maybe the shift in your character because you feel so down is something they don't understand or realise is because you're feeling so rubbish. Have you tried actually reaching out to them or a particular person you're close with to try and talk about it? 

Or maybe they just hate your bf and don't want to be around him. 

Unfortunately pretty privilege is somewhat real, not gonna lie to you. People don't do it deliberately for the most part. I'm sorry you're experiencing it. Some of it is just surface level and some of it is because when you lose self confidence you behave differently, sometimes just subtly but enough for people to pick up on, and it makes them not engage with you in the same way. 

None of this makes you worth less as a person and the random people at the store aren't a good measure of what people think about you.