Might be that I too have anxiety and have experienced these same doomed thoughts, it's horrible and feels like you can't enjoy the relationship because you have this on your mind.
I know this may be completely preachy, but I've found going to a counsellor has helped me immensely. Advice from friends and family can at times be coming from a good place but be more detrimental to your mental health. I see a big difference from my past relationships to the one I'm in now because of this.
Added note: I went to a counsellor who specialised in Gay & Lesbian counselling.
I feel Bann284 is right on the money.