i imagine this was such a difficult thing to write - and i think being honest about how you feel is incredibly important...
i am a single mother too. and it is, as you say, a very demanding and tricky position to be in, practically and emotionally. i absolutely understand your feelings of resentment because the truth is that without your daughter you would be having the career/travelling and so on. and at times, sometimes for a long time, i have felt the same - an odd muddled mix of resentment and love and regret and joy and so on.
i would say just four things. the first is that it is absolutely possible that you are depressed - hardly an unreasonable response given the circumstances - and if you think that even might be the case i think its worth exploring it with your gp. because all the people i know who have been, and have taken antid's sucessfully say they cant believe they waited so long to feel better.
the second is that it does get easier. my dd is nearly five and oh my goodness what a change. things are possible now which simply weren't three years ago - the things we do together are more grown up (cinema on saturday mornings for example) which make me feel less like i'm drowning in child. and when we are out and about, or at a party, i dont have to follow her around in case she tries to fall off the nearest wall or whatever. and if i'm knackered she will happily draw or paint while i read for half an hour. it is less relentless, i guess is my point. and that release makes it much easier to enjoy being together all the time. also - we've had more practise at being us - and i've figured out that if i want to see my friends in the evening i take her with me - she used to fall asleep in the car and i'd carry her in a tuck her up, now i just put her to bed there and carry her asleep in the car when we leave. i imagine this isnt ok in the parenting handbook, but it keeps me sane and, by default, allows me to be a better parent. oh and also - there will be things you can do when your dd is older more easily because you are single - my dd and i are going to india for two months at the end of the year because we can - no-one to answer to, no-one else's job to work around.
the third is that it took me a while to realise that friends with partners, as supportive and kind as they may be, will never really get how tough it is. i found things much easier when i stopped expecting them to get it. i still feel if i knew some other single parents it would, in an unspoken way, be easier.
and the fourth is this - all those parents around you who "seem to be happy, capable copers' arent. not all the time. they are frustrated and trapped and confused and ambiguous some of the time. because you'd be sociopathic if not. so stop seeing perfection everywhere else. it doesnt exist.
the bottom line, for me anyway, is this - would i rather not have my dd. and the answer is no. doesnt make it any easier, but i always come back to that. and you will too.
i really hope you are ok. please feel free to keep in touch if you want to talk more. oh, and i hope this doesnt read like a lecture. i just wanted you to know that other people have felt that way too.
best wishes
x
ps - my dd has also been something of a barometer where boys are concerned. my feeling is that anyone who has a problem with me being a mother wouldnt have been good enough even if i wasnt.