Goodness me- thankyou for the overwhelming response here!
I do find some of the replies quite harsh! :-/... I am not a nasty person, just someone over-sensitive,who feels things way too deeply and cares rather too much!)
However alot of the somewhat kinder yet helpfully blunt and honest replies have made me realise that yes alot of all this probably has been caused by my insecurities, trust and control issues.'Best friend' and 'enemy' probably do make it all sound rather immature, and probably weren't wise words to use, but I am not generally an immature person, just that side does show when I am angry as I struggle to handle my emotions in a very mature way.
My father was very controlling over me as a child, and i was always under alot of pressure to behave how he wanted, and have experienced a fair bit of rejection from those around me, which has made me feel like i can't trust people to genuinely care about me and to always worry that they 'don't really like me underneath'.Thats why this seems a big deal to me, as i worried it meant 'H' didnt actually care for me.
I have had jealousy and control issues in friendships since I was about 6 years old, and I guess it's something I've never managed to properly address, and probably should get some help with.I have just always felt that when my friends get to know each other, they seem to get close and detach from me, and worry S might try to turn H against me if they are on good terms I suppose :-/
S and I had a good friendship until C and another girl joined the mix, then for some reason I always felt like the odd one out and inadequate.I guess I was scared they would turn her against me,so became controlling and pressurising towards her as i was scared of losing her, but it backfired and had the opposite effect.Because I was always paranoid about her not liking me and was probably very needy and clingy.I am an only child who had hardly any family either,and have always invested heavily in friends, probably trying to make them more like a sisters.
I can assure you S and I had nothing more than a platonic relationship (in my eyes anyway, and hers too as far as I know) although she was bisexual I am hetrosexual.S struggled to maintain relationships with boyfriends, as did I for a long time, but I eventually settled down, and seeing me getting married and planning to start a family which was what she wanted too must have hurt, although I always tried hard never to rub it in her face, maybe it was too much as she was feeling down about all that not long before our friendship ended.She also had a brief relationship with my husband's mate not long before, and was very upset when he ended things, which probably didn't help either.
I guess we both had our issues with one another's lives and behaviours.
I will be apologising to H as, like someone sensibly said, if I lose her too then it is just letting S continue to hurt me.It might be too late as alot was said between us, but I know we still care about each other so perhaps if I accept responsibility for doing wrong then perhaps she may reconsider.I really do hope so.