So I have two sad Bilbo theories/headcannons:
• So we know Bilbo’s parents are dead, and we don’t know how long for. So I’m guessing they died around when Bilbo was in his 40’s to even maybe late 30’s (but that may be pushing it). But so we know he’s gotten used to be alone in his smial due to his parents passing, and he’s not the most sociable, so he could be touch starved.
(This bit more headcannon I think) and then when he’s suddenly taken out of his lonely, touch deprived life onto the journey with the dwarves, we see they’re very “touch is our love language” kinda thing to put it. And so when the company finally all accept him (I see this mainly after him saving Thorin) they like pat him on the shoulder, brush arms with him, just little touches to show they care for him. He doesn’t know how to like respond to it so every time it happens he freezes up and feels awkward, not knowing how to respond so just pretends it didn’t happen.
I like to think after awhile the company realise this and so try to show him more affection but not overwhelmingly. In a gradual way that so Bilbo gets used to it until he feels comfortable with being touched.
• So back with Bilbo’s parents being dead- so we actually don’t know when they died. It could’ve been quite recent and so Bilbo could still be mourning his parents deaths when on the journey with the dwarves.
I just realised I kept referring to Bungo and Belladonnas deaths happening together. They didn’t it’s just easier to word it and not add more words to the post.