I remember being absolutely horrified after my parents broke up (I was 13/14) and my mum started seeing someone else, having him stay over, etc. It didn't help that he was quite a selfish person and wanted my mum to only do things with him. He had no kids, lived alone etc. and so didn't really get that my 11 year old brother and I were still reeling from the divorce and having some behavioural issues as a result. We were also teen/pre-teen age obviously, so dealing with hormones and the various problems that tend to arise between children and their parents at this age as well. This guy didn't like us at all, was constantly trying to correct our behaviour, and couldn't fathom that we needed our mother to be more available than he wanted her to be, which was a recipe for absolute disaster. After a couple of rubbishy years, he ended up ultimately cheating on our mum, blaming us and labelling us 'miserable kids'. She told him where to go then.
While there was no question that she would always have picked us had it come down to that, witnessing our mother be 'selfish' and think about herself for the first time in our lives was a real shock for us as children. Years later, when I was older, we did talk about it and I told her outright that I had been incredibly hurt by how quickly she had tried to move this person into our lives so soon after the divorce, and that I felt she had made a really bad choice, which had caused me to massively lose respect for her as a teenager. I also acknowledged that I understood why she did it - that she had obviously been unhappy with my dad for a long time and was ready to move on with someone new. The problem was that she failed to realise that the rest of us weren't ready - and as our mother, I believe her duty to us as young people was primarily to make sure our emotional needs were met before she took that step, which she just didn't. Despite being (and still being today) an exemplary and fantastic mum, she was unable to separate her own feelings about our father, the awful divorce, etc. from ours. We had lost a parent and our whole family life as we knew it. We were damaged, too.
I don't know how much, if any, of this seems similar to your situation, but first and foremost you need to talk openly to your daughter. At 17, she is still not going to be emotionally mature/experienced enough to understand that your feelings for your partner have no bearing on your feelings for her at all (presumably). She likely understands sexual/physical desire and feelings at her age, but is presumably unlikely to have been involved in a lengthy and meaningful romantic relationship just yet and will have no concept at all of the way parents feel about their kids. Even though she's almost technically an adult, these concepts come about through experience - experience she just has not had yet. As childish and self-centred as it may seem, she probably needs to know that you are not 'picking' your partner over her and also that you still and always will love her more and like her best, even though you love and like your partner too. My guess would be that she's worrying about this, and hearing the two of you having sex probably feels like it's (almost literally) being rubbed in her face. If you look at it from her standpoint, and especially if you've never had a conversation of this ilk with her, it's probably a very worrying and confusing time for her seeing you happy with someone who ISN'T her.
I'm now 30 and have a good relationship with my mum, who has been in a relationship with a very decent guy for many years now, but for a long time I felt resentful and awkward around her, and you need to avoid that if you can. Talking openly, reassuringly and honestly, and encouraging her to do the same, is the best way to start improving things.
