In other appeals for help and insight I have described a basic problem between my gf and me (36&35 years old). I feel that I have come closer to the issue in that she fears of being replaceable and being manipulated.

She met me in the waning days of a "pickup phase" after a break up. When we had sex the first time after several dates it was verygood and she thanked me for being so considerate of her needs, etc. This sounded like a good start to me and there is something very rewarding in having good sex with somebody who didn't have this experience for some time.

But as time passed by (now 9 months of a relationship) she began second guessing if I might be using good sex to manipulate her. This is quite irritating to me because - even though I like my needs being met and I can be a pain in the behind if they aren't - I simply prefer good and satisfying sex to lackluster sex, I like having sex with somebody I love and I do not use it to further my needs other than having good sex and showing intimacy.

I feel uneasy because of this as I do not see how I earned that lack of trust or - if this is not about me but about her - how I can live with this lack of basic trust that simmers through this.

Thanks!

This is her issue, not yours. If she can't get it under control (to your satisfaction, at least) then you'll have to have a talk with her.

Is there anything at all that's made her start second guessing you? Cheating or flirting? Do you hide your phone, lock your phone, etc... (not that she should be going through your shit anyway, but that could be seen as a barrier for her).

If you've legitimately done nothing to make her doubt you then she's got some trust issues and I guess it depends where you want to take it with her. Since you're in a relationship with her I'd say it's OK to bend a bit on this and work at it with her if she's otherwise a good girl. Invest in her if she's what you want. I don't really think PUA/game is applicable once you've been with someone as long as you have (at least most elements of it).