Feel that my gf's going to 'inevitably' grow beyond me and leave me

I know you keep saying I should love myself first and she's with me for a reason but then why does it feel like she's flirting with him? She even brought up about a girl who asked him out at a party, not knowing he was taken . I think he's perceived as an attractive guy, and to be honest, that she likes him a little. Whether or not enough to end it with me, I don't know.
I don't hate myself but I do feel that, objectively, most things about him are better than me. As much as I would wish it to be true, I don't understand how your value is measured by anything other than your external environment. Even with friends, if they thought they were awesome, that isn't conclusive proof that they're not a flat-out bore or a jerk.

The other fact is, most of my 'friends' have ditched me since I was ill, and probably with good reason. Even with my close ones, it feels like sanitary relationships at arm's length.

It's true that there's always some element of flirtation; I know me and my guy friends do it but the thing is, the borders are all laid out -- they're friends and nothing more could ever happen because it would ruin the friendship. I think it's the same with your girl. Besides, if both parties are taken, the likelihood of something happening is slim to none.

That's not true. Your worth comes from the inside. Just look at all you've achieved and been through, yet you're still here, you're still alive. If I relied on what people thought of me to reflect my worth, I would think of myself as a massive slut and a disappointment. People don't know why you are the way you are, only you do. In my case, the 'slut' thing is because I sleep with a lot of guys. Why? Because I like sex. It's not because I'm 'damaged and need attention'. I just like sex. As for the disappointment thing, my parents tell me I am one because I have tattoos and several piercings. But I've got them because they express my individuality.

Anyone who has ditched you clearly wasn't a true friend.

Thank you Jazzy x
reading this was a bit of a relief. Better yet she is still asking whether I want to go do X and she still says I Love You
I'm hoping I can just see the fun side of her hanging out with her friend Superman, because he is a fun guy-rather than the absolutely disastrous idea 'yep she's going to ditch her own faith and sleep with him just to laugh at me show me how cruel life is'
Hmm

I still need to work on not giving a **** what people think. I guess it's hard because when people say they're worried about you, you can think you're doing something wrong and need to change who you are, rather than what you're thinking

No problem, always here for you

If she's still saying these things then that's proof that she cares, she loves you and she wouldn't hurt you. Besides, guy friends are the best :P I get on better with guys or girls that act like guys. Less b*tchy and more fun.

I know how you feel because I let it affect me for years. It's just about being strong and thinking 'they don't know what I'm going through' and focus on yourself and how you perceive yourself. x

[This is where I get annoying] Is it proof though? I thought it was actually the norm at our age (early twenties?) to say I Love You and then go sleep with someone else. So it's not so much I don't trust her, but I have little faith in the integrity of my entire generation. I'm such an old man :P

I'm glad she has fun with him, he's a nice guy. But as I keep stating, I obviously don't want 'fun' to eventually include ****ing. (I actually don't know anymore whether that's a reasonable boundary to set in a committed relationship, 'don't go bonking someone else behind my back without expecting me to be hurt badly and probably not want you back'. I would have thought so?
So for example, it's OK for them to have banter, hugs, kissing on the cheek would be OK I guess if it was in a brotherly/sisterly sort of way, I'd draw the line at passionately kissing each other, feeling each other up, and if she started calling someone else's name out than mine when we're intimate I'd also want to know what's going on.
Do these seem reasonable boundaries? (I can't believe I'm asking this, to me the answer would be a flat-out Yes but everyone has different boundaries after all)

I didn't even think about boundaries because the notion she could cheat didn't cross my mind until lately, and I want to trust her frankly. For whatever reason I've gone into a relationship thinking that just because my mum and dad split, all relationships fail, and especially at our age.

It's hard but we can do this