I've always been of the view that if a relationship is mutually agreed to be monogamous and for the long-term, then it's absolutely reasonable to conclude that your partner is committing themselves to be your exclusive sexual partner, and therefore is entering into an agreement with you that they will attempt to meet your sexual needs where appropriate.
What form that takes, and what is deemed acceptable sexual behaviour within a relationship is entirely at the discretion of the individuals involved, and we all have different ideas about boundaries and what we accept as reasonable. I do not accept claims that any man who watches his wife undress is perverted, or that touching is sexual harassment, or that requesting sex makes anyone a 'sex pest', but I absolutely do agree that if these things are inappropriate for you as an individual, then of course, you are well within your rights to deem them as unacceptable within your relationships.
People can leave relationships for any reason they choose, so I think that if any of these behaviours cross your line in the sand, then they are perfectly valid reasons for you to leave. However, given that I also believe meeting of sexual needs is a reasonable expectation within a monogamous relationship, I also think it's perfectly reasonable to leave a relationship because your partner withholds sex, has no interest in sex, or does not want you touching them, watching them, or requesting sex.
All of these things are perfectly reasonable sexual behaviours in my opinion, but other people will disagree because other people have different boundaries and different lines in the sand. I don't think it's either realistic or reasonable to resent people simply for expecting their needs to be met by the person who entered into an agreement to do so, but over time people can change. The fundamental thing for me, is that it's unreasonable to expect people to live without their needs being met, or refuse to do your part in that, but then still expect the unfulfilled party to abide by the terms of your agreement when it's actually you who has moved the goalposts.
Again, I don't view any of the specific behaviours described as unacceptable, in fact, for me they're a significant part of my own sexuality and I absolutely expect them if I'm going to deem my relationship sexually healthy, however, I totally accept that other people will take a different view. I do find it odd that some people suggest that requesting sex is being a 'sex pest' when that's within a monogamous relationship. Is the requesting party simply supposed to deny and repress their sexual urges indefinitely, until such time that the offended party signals that a request would be accepted? What if that time never arrives? Of course, nobody should ever feel they are being pestered or harassed constantly for sex by their partner, but then, if you don't ask you don't get, and I take the view that feeling pestered is a sign of incompatibility, not that the requesting party is deviant or unreasonable. The same with touching and watching. Sure, there are times and places where it's inappropriate and undesirable, but in the correct setting I think it's lovely and endearing when my partner gives me a playful smack/squeeze/tickle, it's reciprocated, we both enjoy it and regard it as something that's natural and normal. If you don't appreciate it, perhaps you shouldn't be with someone who does?